memory-graph 0.3.65
Teaching tool and debugging aid in context of references, mutable data types, and shallow and deep copy.
Requires Python: >=3.7

# Installation #
Install (or upgrade) `memory_graph` using pip:
```
pip install --upgrade memory_graph
```
Additionally [Graphviz](https://graphviz.org/download/) needs to be installed.

# Highlights #
![vscode_copying.gif](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/vscode_copying.gif)
Run a live demo in the 👉 [**Memory Graph Web Debugger**](https://memory-graph.com/#breakpoints=8&continues=1&timestep=1.0&play) 👈 now, no installation required!

- learn the right **mental model** to think about Python data (references, mutability, shallow vs deep copy)
- **visualize the structure of your data** to easily understand and debug any data structure
- understand function calls, variable scope, and the **complete program state** through call stack visualization

An example Binary Tree data structure:
![images/bin_tree.gif](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/bin_tree.gif)
Or see it in the [Memory Grah Web Debugger](https://memory-graph.com/#codeurl=https://raw.githubusercontent.com/bterwijn/memory_graph/refs/heads/main/src/bin_tree.py&timestep=0.2&play).

# Videos #
| [![Quick Intro](https://img.youtube.com/vi/23_bHcr7hqo/0.jpg)](https://www.youtube.com/watch?v=23_bHcr7hqo) | [![Mutability](https://img.youtube.com/vi/pvIJgHCaXhU/0.jpg)](https://www.youtube.com/watch?v=pvIJgHCaXhU) |
|:--:|:--:|
| [Quick Intro (3:49)](https://www.youtube.com/watch?v=23_bHcr7hqo) | [Mutability (17:29)](https://www.youtube.com/watch?v=pvIJgHCaXhU) |

# Memory Graph #
For program understanding and debugging, the [memory_graph](https://pypi.org/project/memory-graph/) package can visualize your data, supporting many different data types, including but not limited to:

```python
import memory_graph as mg

class My_Class:

    def __init__(self, x, y):
        self.x = x
        self.y = y

data = [ range(1, 2), (3, 4), {5, 6}, {7:'seven', 8:'eight'},  My_Class(9, 10) ]
mg.show(data)
```
![many_types.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/many_types.png)

Instead of showing the graph on screen you can also render it to an output file (see [Graphviz Output Formats](https://graphviz.org/docs/outputs/)) using for example:

```python
mg.render(data, "my_graph.pdf")
mg.render(data, "my_graph.svg")
mg.render(data, "my_graph.png")
mg.render(data, "my_graph.gv") # Graphviz DOT file
mg.render(data) # renders to default: 'memory_graph.pdf'
```

# Sharing Values #
In Python, assigning a list from variable `a` to variable `b` causes both variables to reference the same list value and thus share it. Consequently, any change applied through one variable will impact the other. This behavior can lead to elusive bugs if a programmer incorrectly assumes that list `a` and `b` are independent.

<table><tr><td> 

```python
import memory_graph as mg

# create the lists 'a' and 'b'
a = [4, 3, 2]
b = a
b.append(1) # changing 'b' changes 'a'

# print the 'a' and 'b' list
print('a:', a)
print('b:', b)

# check if 'a' and 'b' share values
print('ids:', id(a), id(b))
print('identical?:', a is b)

# show all local variables in a graph
mg.show( locals() )
```

</td><td>

![mutable2.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/mutable2.png)

a graph showing `a` and `b` share values

</td></tr></table>

The fact that `a` and `b` share values can not be verified by printing the lists. It can be verified by comparing the identity of both variables using the `id()` function or by using the `is` comparison operator as shown in the program output below, but this quickly becomes impractical for larger programs.
```{verbatim}
a: 4, 3, 2, 1
b: 4, 3, 2, 1
ids: 126432214913216 126432214913216
identical?: True
```
A better way to understand what values are shared is to draw a graph using [memory_graph](https://pypi.org/project/memory-graph/).

# Topics #

[Python Data Model](#python-data-model)

[Call Stack](#call-stack)

[Data Model Exercises](#data-model-exercises)

[Block](#block)

[Debugging](#debugging)

[Data Structure Examples](#data-structure-examples)

[Sorting Algorithms](#sorting-algorithms)

[Bitwise Operators](#bitwise-operators)

[Sliding Puzzle Solver](#sliding-puzzle-solver)

[Configuration](#configuration)

[Introspection](#introspection)

[Graph Depth](#graph-depth)

[Extensions](#extensions)

[Memory Graph Web Debugger](#memory-graph-web-debugger)

[Jupyter Notebook](#jupyter-notebook)

[ipython](#ipython)

[Google Colab](#google-colab)

[Marimo](#marimo)

[Animated GIF](#animated-gif)

[Troubleshooting](#troubleshooting)

[Other Packages](#other-packages)

## Author ##
Bas Terwijn

## Inspiration ##
Inspired by [Python Tutor](https://pythontutor.com/).

The main differences are that running memory_graph locally is a key design choice to support Python Tutor’s [unsupported features](https://github.com/pythontutor-dev/pythontutor/blob/master/unsupported-features.md#unsupported-features) and mirroring the data’s hierarchy improves graph readability.

## Social Media #
* [LinkedIn](https://www.linkedin.com/groups/13244150/)
* [Reddit](https://www.reddit.com/r/Python_memory_graph/)

## Supported by ##
<img src="https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/uva.png" alt="University of Amsterdam" width="600">

___
___

# Python Data Model #
Learn the right **mental model** to think about Python data. The [Python Data Model](https://docs.python.org/3/reference/datamodel.html) makes a distiction between immutable and mutable types:

* **immutable**: bool, int, float, complex, str, tuple, bytes, frozenset
* **mutable**: list, set, dict, classes, ... (most other types)


## Immutable Type ##
In the code below variable `a` and `b` both reference the same tuple value (4, 3, 2). A tuple is an **immutable** type and therefore when we change variable `b` its value **cannot** be mutated in place, and thus an automatic copy is made and `a` and `b` each reference their own value afterwards.

```python
import memory_graph as mg

a = (4, 3, 2)
b = a
mg.render(locals(), 'immutable1.png')

b += (1,)
mg.render(locals(), 'immutable2.png')
```
| ![mutable1.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/immutable1.png) | ![mutable2.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/immutable2.png) |
|:-----------------------------------------------------------:|:-------------------------------------------------------------:|
| immutable1.png | immutable2.png |


## Mutable Type ##
With mutable types the result is different. In the code below variable `a` and `b` both reference the same `list` value [4, 3, 2]. A `list` is a **mutable** type and therefore when we change variable `b` its value **can** be mutated in place and thus `a` and `b` both reference the same new value afterwards. Thus changing `b` also changes `a` and vice versa. Sometimes we want this but other times we don't and then we will have to make a copy ourselfs so that `a` and `b` are independent.

```python
import memory_graph as mg

a = [4, 3, 2]
b = a
mg.render(locals(), 'mutable1.png')

b += [1]  # equivalent to:  b.append(1)
mg.render(locals(), 'mutable2.png')
```
| ![mutable1.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/mutable1.png) | ![mutable2.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/mutable2.png) |
|:-----------------------------------------------------------:|:-------------------------------------------------------------:|
| mutable1.png | mutable2.png |

One practical reason why Python makes the distinction between mutable and immutable types is that a value of a mutable type can be large, making it inefficient to copy each time we change it. Values of immutable type generally don't need to change as much, or are small, making copying less of a concern.

## Copying Values of Mutable Type ##
Python offers three different "copy" options that we will demonstrate using a nested list:

```python
import memory_graph as mg
import copy

a = [ [1, 2], ['x', 'y'] ]  # a nested list (a list containing lists)

# three different ways to make a "copy" of 'a':
c1 = a
c2 = copy.copy(a)  # for list equivalent to:  a.copy() a[:] list(a)
c3 = copy.deepcopy(a)

mg.show(locals())
```

* `c1` is an **assignment**, nothing is copied, all the values are shared
* `c2` is a **shallow copy**, only the first value is copied, all the underlying values are shared
* `c3` is a **deep copy**, all the values are copied, nothing is shared

![copy_mutbale.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/copy_mutable.png)

Or see it in the [Memory Grah Web Debugger](https://memory-graph.com/#codeurl=https://raw.githubusercontent.com/bterwijn/memory_graph/refs/heads/main/src/copies.py&play).

## Custom Copy ##
We can write our own custom copy function or method in case the three standard "copy" options don't do what we want. For example, in the code below the `custom_copy()` method of My_Class copies the `digits` but shares the `letters` between two objects.

```python
import memory_graph as mg
import copy

class My_Class:

    def __init__(self):
        self.digits = [1, 2]
        self.letters = ['x', 'y']

    def custom_copy(self): 
        """ Copies 'digits' but shares 'letters'. """
        c = copy.copy(self)
        c.digits = copy.copy(self.digits)
        return c

a = My_Class()
b = a.custom_copy()

mg.show(locals())
```
![copy_method.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/copy_method.png)

Or see it in the [Memory Grah Web Debugger](https://memory-graph.com/#codeurl=https://raw.githubusercontent.com/bterwijn/memory_graph/refs/heads/main/src/custom_copy.py&breakpoints=15&continues=1&play).

## Name Rebinding ##
When `a` and `b` share a mutable value, then changing the value of `b` changes the value of `a` and vice versa. However, reassigning `b` does not change `a`. When you reassign `b`, you only **rebind** the name `b` to another value without affecting any other variable.

```python
import memory_graph as mg

a = [4, 3, 2]
b = a
mg.render(locals(), 'rebinding1.png')

b += [1]        # changes the value of 'b' and 'a'
b = [100, 200]  # rebinds 'b' to another value, 'a' is unaffected
mg.render(locals(), 'rebinding2.png')
```
| ![rebinding1.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/rebinding1.png) | ![rebinding2.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/rebinding2.png) |
|:-----------------------------------------------------------:|:-------------------------------------------------------------:|
| rebinding1.png | rebinding2.png |

Or see it in the [Memory Grah Web Debugger](https://memory-graph.com/#codeurl=https://raw.githubusercontent.com/bterwijn/memory_graph/refs/heads/main/src/rebind.py&play).

## Copying Values of Immutable Type ## 
Because a value of immutable type will be copied automatically when it is changed, there is no need to copy it beforehand. Therefore, a shallow or deep copy of a value of immutable type will result in just an assignment to save on the time needed to make the copy and the space (=memory) needed to store the values.

```python
import memory_graph as mg
import copy

a = ( (1, 2), ('x', 'y') ) # a nested tuple

# three different ways to make a "copy" of 'a':
c1 = a
c2 = copy.copy(a)
c3 = copy.deepcopy(a)

mg.show(locals())
```
![copy_immutbale.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/copy_immutable.png)

## Copying a Mix of Mutable and Immutable Values ##
When copying a mix of values of mutable and immutable type, to save on time and space, a deep copy will try to copy as few values of immutable type as possible in order to copy each value of mutable type.
```python
import memory_graph as mg
import copy

a = ( [1, 2], ('x', 'y') ) # mix of mutable and immutable

# three different ways to make a "copy" of 'a':
c1 = a
c2 = copy.copy(a)
c3 = copy.deepcopy(a)

mg.show(locals())
```
![copy_mix.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/copy_mix.png)

# Call Stack #
The `mg.stack()` function retrieves the entire call stack, including the local variables for each function on the stack. This enables us to understand function calls, variable scope, and the **complete program state** through call stack visualization. By examining the graph, we can see whether local variables from different function calls share data. For instance, consider the function `add_one()` which adds the value `1` to each of its parameters `a`, `b`, and `c`.

```python
import memory_graph as mg

def add_one(a, b, c):
    a += [1]
    b += (1,)
    c += [1]
    mg.show(mg.stack())

a = [4, 3, 2]
b = (4, 3, 2)
c = [4, 3, 2]
add_one(a, b, c.copy())

print(f"a:{a} b:{b} c:{c}")
```
![add_one.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/add_one.png)

Or see it in the [Memory Grah Web Debugger](https://memory-graph.com/#codeurl=https://raw.githubusercontent.com/bterwijn/memory_graph/refs/heads/main/src/function_call.py&play).

In the printed output we see that only `a` is changed as a result of the function call:
```
a:[4, 3, 2, 1] b:(4, 3, 2) c:[4, 3, 2]
```
This is because `b` is of immutable type 'tuple' so its value gets copied automatically when it is changed. And because the function is called with a copy of `c`, its original value is not changed by the function. The value of variable `a` is the only value of mutable type that is shared between the root stack frame **'0: \<module>'** and the **'1: add_one'** stack frame of the function call so only that variable is affected as a result of calling the function. The other changes remain confined to the local variables of the ```add_one()``` function.

## Function Call That Changes 'int' Value ##
Even though `int` is an immutable type, so an `int` value can not be changed by directly passing it to a function, we can still change it by wrapping it in a mutable container.

```python
import memory_graph as mg

def add_one(a, b):
    a += 1     # change remains confined to 'a' in the add_one function
    b[0] += 1  # change also affects 'b' outside of the add_one function
    mg.show(mg.stack())

a = 10
b = [10]  # wrap in a value of mutable type list
add_one(a, b)

print(f"a:{a} b:{b[0]}")
```
![wap_int.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/wrap_int.png)
```
a:10 b:11
```
Or see it in the [Memory Grah Web Debugger](https://memory-graph.com/#codeurl=https://raw.githubusercontent.com/bterwijn/memory_graph/refs/heads/main/src/wrap.py&breakpoints=5&continues=1&play)

The effect of calling `add_one()` is that `b[0]` increases by 1, while `a` is unaffected.

# Data Model Exercises #

Now is a good time to practice with Python Data Model concepts. Here are [some exercises](https://github.com/bterwijn/memory_graph_videos/blob/main/exercises/exercises.md) on references, mutability, copies, and function calls.

# Block #
It is often helpful to temporarily block program execution to inspect the graph. For this we can use the `mg.block()` function:

```python
mg.block(fun, arg1, arg2, ...) 
```

This function:
* first executes `fun(arg1, arg2, ...)`
* then prints the current source location in the program
* then blocks execution until the &lt;Enter&gt; key is pressed
* finally returns the return value of the `fun()` call

## Recursion ##
The call stack is also helpful to visualize how recursion works. Here we use `mg.block()` to show each step of how recursively `factorial(4)` is computed:

```python
import memory_graph as mg

def factorial(n):
    mg.block(mg.show, mg.stack())
    if n==0:
        return 1
    result = n * factorial(n-1)
    mg.block(mg.show, mg.stack())
    return result

print( factorial(4) )
```
![factorial.gif](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/factorial.gif)

and the result is: 1 x 2 x 3 x 4 = 24

Or see it in the [Memory Grah Web Debugger](https://memory-graph.com/#codeurl=https://raw.githubusercontent.com/bterwijn/memory_graph/refs/heads/main/src/factorial.py&timestep=1.0&play).

## Binary Conversion ##
A more interesting recursive example is function `binary()` that converts a integer from decimal to binary representation. 
```python
import memory_graph as mg
mg.config.type_to_horizontal[list] = True  # horizontal lists

def binary(value: int) -> list[int]:
    mg.block(mg.show(), mg.stack())
    if value == 0:
        return []
    quotient, remainder = divmod(value, 2)
    result = binary(quotient) + [remainder]
    mg.block(mg.show(), mg.stack())
    return result

print( binary(100) )
```
![factorial.gif](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/binary.gif)
```
[1, 1, 0, 0, 1, 0, 0]
```

Or see it in the [Memory Grah Web Debugger](https://memory-graph.com/#codeurl=https://raw.githubusercontent.com/bterwijn/memory_graph/refs/heads/main/src/binary_convert.py&timestep=1.0&play).

## Power Set ##
A more complex recursive example is function `power_set()` where lists are shared by different function calls. A power set is the set of all subsets of a collection of values.

```python
import memory_graph as mg

def get_subsets(subsets, data, i, subset):
    mg.block(mg.show, mg.stack())
    if i == len(data):
        subsets.append(subset.copy())
        return
    subset.append(data[i])
    get_subsets(subsets, data, i+1, subset)  #    do include data[i]
    subset.pop()
    get_subsets(subsets, data, i+1, subset)  # don't include data[i]
    mg.block(mg.show, mg.stack())

def power_set(data):
    subsets = []
    get_subsets(subsets, data, 0, [])
    return subsets

print( power_set(['a', 'b', 'c']) )
```

![power_set.gif](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/power_set.gif)
```
[['a', 'b', 'c'], ['a', 'b'], ['a', 'c'], ['a'], ['b', 'c'], ['b'], ['c'], []]
```

Or see it in the [Memory Grah Web Debugger](https://memory-graph.com/#codeurl=https://raw.githubusercontent.com/bterwijn/memory_graph/refs/heads/main/src/power_set.py&timestep=1.0&play).

## Invocation Tree ##
The memory_graph package visualizes data at the currect time, but to better understand recursion it can also be helpful to visualize different function calls over time. This is what the [invocation_tree](https://github.com/bterwijn/invocation_tree?tab=readme-ov-file#installation) package does.

See the power_set example in the [Invocation Tree Web Debugger](https://www.invocation-tree.com/#codeurl=https://raw.githubusercontent.com/bterwijn/memory_graph/refs/heads/main/src/power_set.py&timestep=1.0&play).

# Debugging #

For the best debugging experience with memory_graph set for example expression:
```
mg.render(locals(), "my_graph.pdf")
```
as a **watch** in a debugger tool such as the integrated debugger in Visual Studio Code. Then open the "my_graph.pdf" output file to continuously see all the local variables while debugging. This avoids having to add any memory_graph `show()` or `render()` calls to your code.

## Call Stack in Watch Context ##
The ```mg.stack()``` doesn't work well in **watch** context in most debuggers because debuggers introduce additional stack frames that cause problems. Use these alternative functions for various debuggers to filter out these problematic stack frames:

| debugger | function to get the call stack in 'watch' context |
|:---|:---|
| [pdb](https://docs.python.org/3/library/pdb.html), [pudb](https://pypi.org/project/pudb/) | `mg.stack_pdb()` |
| [Visual Studio Code](https://code.visualstudio.com/docs/languages/python) | `mg.stack_vscode()` |
| [Cursor AI](https://www.cursor.com/) | `mg.stack_cursor()` |
| [PyCharm](https://www.jetbrains.com/pycharm/) | `mg.stack_pycharm()` |
| [Wing](https://wingware.com/) | `mg.stack_wing()` |

![vscode_copying.gif](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/vscode_copying.gif)
See the [Quick Intro (3:49)](https://www.youtube.com/watch?v=23_bHcr7hqo) video for the setup.

## Other Debuggers ##
For other debuggers, invoke this function within the **watch** context. Then, in the "call_stack.txt" file, identify the slice of functions you wish to include as stack frames in the call stack.
```
mg.save_call_stack("call_stack.txt")
```
Then to get the call stack use:
```
mg.stack_slice(begin_functions : list[(str,int)] = [],
               end_functions : list[str] = ["<module>"],
               stack_index: int = 0)
```
with these parameters that determine the begin and end index of the slice of stack frames in the call stack:
* begin_functions: list of (function-name, offset), begins at the index of the first 'function-name' that is found in the call stack with additional 'offset', otherwise begins at index 0
* end_functions: list of function-names, ends at the index of the first 'function-name' that is found in the call stack after begin index (inclusive), otherwise ends at the last index
* stack_index: number of frames removed at the beginning

## Debugging without Debugger Tool ##

To simplify debugging without a debugger tool, we offer these alias functions that you can insert into your code at the point where you want to visualize a graph:

| alias | purpose | function call |
|:---|:---|:---|
| `mg.sl()` | **s**how **l**ocal variables | `mg.show(locals())` |
| `mg.ss()` | **s**how the call **s**tack | `mg.show(mg.stack())` |
| `mg.bsl()` | **b**lock after **s**howing **l**ocal variables | `mg.block(mg.show, locals())` |
| `mg.bss()` | **b**lock after **s**howing the call **s**tack | `mg.block(mg.show, mg.stack())` |
| `mg.rl()` | **r**ender **l**ocal variables | `mg.render(locals())` |
| `mg.rs()` | **r**ender the call **s**tack | `mg.render(mg.stack())` |
| `mg.brl()` | **b**lock after **r**endering **l**ocal variables | `mg.block(mg.render, locals())` |
| `mg.brs()` | **b**lock after **r**endering the call **s**tack | `mg.block(mg.render, mg.stack())` |
| `mg.l()` | same as `mg.bsl()` |  |
| `mg.s()` | same as `mg.bss()` |  |

For example, executing this program:

```python
from memory_graph as mg

squares = []
squares_collector = []
for i in range(1, 6):
    squares.append(i**2)
    squares_collector.append(squares.copy())
    mg.l() # block after showing local variables
```
and pressing &lt;Enter&gt; a number of times, results in:

![debugging.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/debugging.gif)

# Data Structure Examples #
Package memory_graph can **visualize the structure of your data** to easily understand and debug data structures, some examples:

## Circular Doubly Linked List ##
```python
import memory_graph as mg
import random
random.seed(0)  # use same random numbers each run

class Linked_List:
    """ Circular doubly linked list """

    def __init__(self, value=None, 
                 prev=None, next=None):
        self.prev = prev if prev else self
        self.value = value
        self.next = next if next else self

    def add_back(self, value):
        if self.value == None:
            self.value = value 
        else:
            new_node = Linked_List(value,
                                   prev=self.prev,
                                   next=self)
            self.prev.next = new_node
            self.prev = new_node

linked_list = Linked_List()
n = 100
for i in range(n):
    value = random.randrange(n)
    linked_list.add_back(value)
    mg.block(mg.show, locals())  # <--- draw locals
```
![linked_list.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/linked_list.png)

### Linked List in Cursor AI ###
Here we show values being added to a Linked List in Cursor AI. When adding the last value '5' we "Step Into" the code to show more of the details.
![linked_list.gif](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/linked_list.gif)

Or see it in the [Memory Grah Web Debugger](https://memory-graph.com/#codeurl=https://raw.githubusercontent.com/bterwijn/memory_graph/refs/heads/main/src/linked_list.py&timestep=0.2&play).

## Binary Tree ##
```python
import memory_graph as mg
import random
random.seed(0) # use same random numbers each run

class BinTree:

    def __init__(self, value=None, smaller=None, larger=None):
        self.smaller = smaller
        self.value = value
        self.larger = larger

    def add(self, value):
        if self.value is None:
            self.value = value
        elif value < self.value:
            if self.smaller is None:
                self.smaller = BinTree(value)
            else:
                self.smaller.add(value)
        else:
            if self.larger is None:
                self.larger = BinTree(value)
            else:
                self.larger.add(value)
        mg.block(mg.show, mg.stack())  # <--- draw stack

tree = BinTree()
n = 100
for i in range(n):
    value = random.randrange(n)
    tree.add(value)
```
![bin_tree.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/bin_tree.png)

### Binary Tree in Visual Studio Code ###
Here we show values being inserted in a Binary Tree in Visual Studio Code. When inserting the last value '29' we "Step Into" the code to show the recursive implementation.
![images/bin_tree.gif](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/bin_tree.gif)

See it in the [Memory Grah Web Debugger](https://memory-graph.com/#codeurl=https://raw.githubusercontent.com/bterwijn/memory_graph/refs/heads/main/src/bin_tree.py&timestep=0.2&play) or see the more advanced [Multiway Tree](https://memory-graph.com/#codeurl=https://raw.githubusercontent.com/bterwijn/memory_graph/refs/heads/main/src/multiway_tree.py&breakpoints=19,33&continues=1&timestep=0.2&play) with more than two children per node, making the tree less deep and more efficient.

## Hash Set ##
```python
import memory_graph as mg
import random
random.seed(0)  # use same random numbers each run

class HashSet:

    def __init__(self, capacity=15):
        self.buckets = [None] * capacity

    def add(self, value):
        index = hash(value) % len(self.buckets)
        if self.buckets[index] is None:
            self.buckets[index] = []
        bucket = self.buckets[index]
        bucket.append(value)
        mg.block(mg.show, locals())  # <--- draw locals

    def contains(self, value):
        index = hash(value) % len(self.buckets)
        if self.buckets[index] is None:
            return False
        return value in self.buckets[index]

    def remove(self, value):
        index = hash(value) % len(self.buckets)
        if self.buckets[index] is not None:
            self.buckets[index].remove(value)
        
hash_set = HashSet()
n = 100
for i in range(n):
    new_value = random.randrange(n)
    hash_set.add(new_value)
```
![hash_set.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/hash_set.png)

### Hash Set in PyCharm ###
Here we show values being inserted in a HashSet in PyCharm. When inserting the last value '44' we "Step Into" the code to show more of the details.
![images/hash_set.gif](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/hash_set.gif)

Or see it in the [Memory Grah Web Debugger](https://memory-graph.com/#codeurl=https://raw.githubusercontent.com/bterwijn/memory_graph/refs/heads/main/src/hash_set.py&breakpoints=32&continues=1&timestep=0.5&play).


# Sorting Algorithms #

Visualization of different sorting algorithms in Memory Graph Web Debugger.
![selections_sort.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/selection_sort.gif)

- [selection sort](https://memory-graph.com/#codeurl=https://raw.githubusercontent.com/bterwijn/memory_graph/refs/heads/main/src/selection_sort.py&breakpoints=13,27&continues=1&timestep=0.2&play)
- [insertion sort](https://memory-graph.com/#codeurl=https://raw.githubusercontent.com/bterwijn/memory_graph/refs/heads/main/src/insertion_sort.py&breakpoints=13,29&continues=1&timestep=0.2&play)
- [bubble sort](https://memory-graph.com/#codeurl=https://raw.githubusercontent.com/bterwijn/memory_graph/refs/heads/main/src/bubble_sort.py&breakpoints=29,38&continues=1&timestep=0.2&play)
- [cocktail shaker sort](https://memory-graph.com/#codeurl=https://raw.githubusercontent.com/bterwijn/memory_graph/refs/heads/main/src/cocktail_sort.py&breakpoints=16,45&continues=1&timestep=0.2&play)


# Bitwise Operators #
In this configuration example we show the decimal, binary and [two's complement representation](https://www.cs.cornell.edu/~tomf/notes/cps104/twoscomp.html) representation of `int` values of dictionary subclass `Bits` to show the result of [bitwise operators](https://docs.python.org/3/library/stdtypes.html?utm_source=chatgpt.com#bitwise-operations-on-integer-types). The `~` (inverse) operator can be a bit confusing if not shown with two's complement representation.

- [bitwise operators](https://memory-graph.com/#codeurl=https://raw.githubusercontent.com/bterwijn/memory_graph/refs/heads/main/src/bitwise_operators.py&breakpoints=22&continues=1&play)

![bitwise_operators.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/bitwise_operators.png)


# Sliding Puzzle Solver #

A sliding puzzle solver as a challenging example showing how memory_graph deals with large amounts of data. Click "Continue" to step through the breadth-first search generations until a solution path is found:

- [sliding puzzle solver](https://memory-graph.com/#codeurl=https://raw.githubusercontent.com/bterwijn/memory_graph/refs/heads/main/src/sliding_puzzle.py&breakpoints=17,27,29,40&continues=1)

![sliding_puzzle.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/sliding_puzzle.png)


# Configuration #
Different aspects of memory_graph can be configured. The default configuration can be reset by calling 'mg.config_default.reset()'. The Memory Graph Web Debugger gives examples of the [most important configurations](https://memory-graph.com/#codeurl=https://raw.githubusercontent.com/bterwijn/memory_graph/refs/heads/main/src/config.py&play).

- ***mg.config.reopen_viewer*** : bool
  - If True the viewer is reopened each time show() is called, this might change window focus, default True.

- ***mg.config.render_filename*** : str
  - The default filename to render to, default 'memory_graph.pdf'.

- ***mg.config.type_labels*** : bool
  - If True the type of each node is shown as label, default True.

- ***mg.config.block_prints_location*** : bool
  - If True the source location is printed in block(), default True.
  
- ***mg.config.press_enter_message*** : str
  - Message to ask user to press &lt;Enter&gt; in block(), set to None to disable.

- ***mg.config.max_string_length*** : int
  - The maximum length of strings shown in the graph. Longer strings will be truncated.

- ***mg.config.embedded_types*** : set[type]
  - Holds all types for which no separate node is drawn but that are embedded in their parent Node.

- ***mg.config.embedded_key_types*** : set[type]
  - Holds all types that are embedded as key in a Node_Key_Value node, even when not in 'embedded_types'.

- ***mg.config.embedding_types*** : set[type]
  - Holds all dictionary types that embed their key-value tuple children.

- ***mg.config.no_index_types*** : set[type]
  - Holds all types like 'set' and 'frozenset' that should not have indices as Node_Linear.

- ***mg.config.type_to_node*** : dict[type, fun(data) -> Node]
  - Determines how a data type is converted to a Node subclass for visualization in the graph.

- ***mg.config.type_to_color*** : dict[type, color]
  - Maps a type to the [graphviz color](https://graphviz.org/doc/info/colors.html) it gets in the graph. 

- ***mg.config.type_to_horizontal*** : dict[type, bool]
  - Maps a type to its orientation for Node_Linear and Node_Key_Value. Use 'True' for horizontal and 'False' for vertical. If not specified these nodes vertical unless they have references to children.

- ***mg.config.type_to_slicer*** : dict[type, int]
  - Maps a type to a Slicer. A slicer determines how many elements of a data type are shown in the graph to prevent the graph from getting too big. 'Slicer()' does no slicing, 'Slicer(1,2,3)' shows just 1 element at the beginning, 2 in the middle, and 3 at the end.

- ***mg.config.max_graph_depth*** : int
  - The maxium depth of the graph with default value 1000.

- ***mg.config.graph_cut_symbol*** : str
  - The symbol indicating where the graph is cut short with default `✂`.
  
- ***mg.config.type_to_depth*** : dict[type, int]
  - Maps a type to graph depth to limit the graph size.

- ***mg.config.max_missing_edges*** : int
  - Maximum number of missing edges that are shown with default value 2. Dashed references are used to indicate that there are more references to a node than are shown.

- ***mg.config.fontname*** : str
  - The font used in the graph, default 'Times-Roman' (widely available on the web).

- ***mg.config.fontsize*** : str
  - The font size used in the graph, default '14'.


## Simplified Graph ##
Memory_graph simplifies the visualization (and the viewer's mental model) by **not** showing separate nodes for immutable types like `bool`, `int`, `float`, `complex`, and `str` by default. This simplification can sometimes be slightly misleading. As in the example below, after a shallow copy, lists `a` and `b` technically share their `int` values, but the graph makes it appear as though `a` and `b` each have their own copies. However, since `int` is immutable, this simplification will never lead to unexpected changes (changing `a`'s ints won’t affect `b`) so will never result in bugs.

The simplification strikes a balance: it is slightly misleading but keeps the graph clean and easy to understand and focuses on the mutable types where unexpected changes can occur. This is why it is the default behavior. If you do want to show separate nodes for `int` values, such as for educational purposes, you can simply remove `int` from the `mg.config.embedded_types` set:
```python
import memory_graph as mg

a = [100, 200, 300]
b = a.copy()
mg.render(locals(), 'embedded1.png')

mg.config.embedded_types.remove(int)  # now show separate nodes for int values

mg.render(locals(), 'embedded2.png')
```
| ![embedded1](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/embedded1.png) | ![embedded2](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/embedded2.png) |
|:-----------------------------------------------------------:|:-------------------------------------------------------------:|
| embedded1.png — simplified | embedded2.png — technically correct |

Additionally, the simplification hides away the [reuse of small int values \[-5, 256\]](https://docs.python.org/3/c-api/long.html#c.PyLong_FromLong) in the current CPython implementation, an optimization that might otherwise confuse beginner Python programmers. For instance, after executing `a[1]+=1; b[1]+=1` the `201` value is, maybe surprisingly, still shared between `a` and `b`, whereas executing `a[2]+=1; b[2]+=1` does not result in sharing the `301` value. Similarly CPython uses [String Interning](https://python-reference.readthedocs.io/en/latest/docs/functions/intern.html) to reuse small strings.

# Introspection #
Sometimes the introspection fails or is not as desired. For example the `bintrees.avltree.Node` object doesn't show any attributes in the graph below.

```python
import memory_graph as mg
import bintrees

# Create an AVL tree
tree = bintrees.AVLTree()
tree.insert(10, "ten")
tree.insert(5, "five")
tree.insert(20, "twenty")
tree.insert(15, "fifteen")

mg.show(locals())
```
![extension_numpy.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/avltree_fail.png)

## All attributes using dir() ##
A useful start is to give it some color, show the list of all its attributes using `dir()`, and setting an empty Slicer to see the attribute list in full.

```python
import memory_graph as mg
import bintrees

# Create an AVL tree
tree = bintrees.AVLTree()
tree.insert(10, "ten")
tree.insert(5, "five")
tree.insert(20, "twenty")
tree.insert(15, "fifteen")

mg.config.type_to_color[bintrees.avltree.Node] = "sandybrown"
mg.config.type_to_node[bintrees.avltree.Node] = lambda data: mg.Node_Linear(data,
                                                dir(data))
mg.config.type_to_slicer[bintrees.avltree.Node] = mg.Slicer()

mg.show(locals())
```
![avltree_dir.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/avltree_dir.png)

Next figure out what the attributes are you want to graph and choose a Node type, there are four options:

## 1) Node_Leaf ##
Node_Leaf is a node with no children and shows just a single value.
```python
import memory_graph as mg
import bintrees

# Create an AVL tree
tree = bintrees.AVLTree()
tree.insert(10, "ten")
tree.insert(5, "five")
tree.insert(20, "twenty")
tree.insert(15, "fifteen")

mg.config.type_to_color[bintrees.avltree.Node] = "sandybrown"
mg.config.type_to_node[bintrees.avltree.Node] = lambda data: mg.Node_Leaf(data,
                                                f"key:{data.key} value:{data.value}")

mg.show(locals())
```
![avltree_leaf.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/avltree_leaf.png)

## 2) Node_Linear ##
Node_Linear shows multiple values in a line like a list.
```python
import memory_graph as mg
import bintrees

# Create an AVL tree
tree = bintrees.AVLTree()
tree.insert(10, "ten")
tree.insert(5, "five")
tree.insert(20, "twenty")
tree.insert(15, "fifteen")

mg.config.type_to_color[bintrees.avltree.Node] = "sandybrown"
mg.config.type_to_node[bintrees.avltree.Node] = lambda data: mg.Node_Linear(data,
                                                ['left:', data.left,
                                                 'key:', data.key,
                                                 'value:', data.value,
                                                 'right:', data.right] )

mg.show(locals())
```
![avltree_linear.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/avltree_linear.png)

## 3) Node_Key_Value ##
Node_Key_Value shows key-value pairs like a dictionary. Note the required `items()` call at the end.
```python
import memory_graph as mg
import bintrees

# Create an AVL tree
tree = bintrees.AVLTree()
tree.insert(10, "ten")
tree.insert(5, "five")
tree.insert(20, "twenty")
tree.insert(15, "fifteen")

mg.config.type_to_color[bintrees.avltree.Node] = "sandybrown"
mg.config.type_to_node[bintrees.avltree.Node] = lambda data: mg.Node_Key_Value(data,
                                                {'left': data.left,
                                                 'key': data.key,
                                                 'value': data.value,
                                                 'right': data.right}.items() )

mg.show(locals())
```
![avltree_key_value.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/avltree_key_value.png)

## 4) Node_Table ##
Node_Table shows all the values as a table.
```python
import memory_graph as mg
import bintrees

# Create an AVL tree
tree = bintrees.AVLTree()
tree.insert(10, "ten")
tree.insert(5, "five")
tree.insert(20, "twenty")
tree.insert(15, "fifteen")

mg.config.type_to_color[bintrees.avltree.Node] = "sandybrown"
mg.config.type_to_node[bintrees.avltree.Node] = lambda data: mg.Node_Table(data,
                                                [[data.key, data.value],
                                                 [data.left, data.right]] )

mg.show(locals())
```
![avltree_table.png](https://raw.githubusercontent.com/bterwijn/memory_graph/main/images/avltree_table.png)

## Binary Search ##
For binary search we can use a List_View class to represent a particular sublist without making a list copy.

```python
import memory_graph as mg
import random
random.seed(2)  # same random numbers each run

class List_View:

    def __init__(self, lst, begin, end):