Repository: TheAlgorithms/Python

Issue:
[mypy] Need help to fix all `mypy` errors in the codebase
# Just one left to fix...
https://github.com/TheAlgorithms/Python/blob/master/mypy.ini#L5
* [x] other/least_recently_used.py
* [x] other/lfu_cache.py #5755
* [x] other/lru_cache.py #5755

---

__UPDATE:__ Our GitHub Actions now run `mypy --ignore-missing-imports` excluding those directories that fail that test.
* https://github.com/TheAlgorithms/Python/blob/master/mypy.ini#L5

Currently, we are not running `mypy` in our regular CI tests as there are a lot of errors in the entire codebase, which needs to be fixed. This won't be a one-person job, so we are asking for help from you. I cannot paste the entire message in here as there are around 600 of them, so here's just a gist of it:

```console
$ mypy --ignore-missing-imports .
strings/word_occurrence.py:17: error: Need type annotation for 'occurrence'
strings/min_cost_string_conversion.py:36: error: No overload variant of "__setitem__" of "list" matches argument types "int", "str"
strings/min_cost_string_conversion.py:36: note: Possible overload variants:
strings/min_cost_string_conversion.py:36: note:     def __setitem__(self, int, int) -> None
strings/min_cost_string_conversion.py:36: note:     def __setitem__(self, slice, Iterable[int]) -> None
strings/min_cost_string_conversion.py:40: error: No overload variant of "__setitem__" of "list" matches argument types "int", "str"
strings/min_cost_string_conversion.py:40: note: Possible overload variants:
strings/min_cost_string_conversion.py:40: note:     def __setitem__(self, int, int) -> None
strings/min_cost_string_conversion.py:40: note:     def __setitem__(self, slice, Iterable[int]) -> None
...
backtracking/n_queens_math.py:109: error: List comprehension has incompatible type List[str]; expected List[int]
backtracking/n_queens_math.py:110: error: Argument 1 to "append" of "list" has incompatible type "List[int]"; expected "List[str]"
backtracking/n_queens_math.py:149: error: Need type annotation for 'boards' (hint: "boards: List[<type>] = ...")
backtracking/minimax.py:15: error: "list" is not subscriptable, use "typing.List" instead
backtracking/knight_tour.py:6: error: "tuple" is not subscriptable, use "typing.Tuple" instead
backtracking/knight_tour.py:6: error: "list" is not subscriptable, use "typing.List" instead
...
```

# Guidelines to follow:

- Please make sure you read the [Contributing Guidelines](https://github.com/TheAlgorithms/Python/blob/master/CONTRIBUTING.md) first.
- Please submit a fix for a maximum of 3 files at a time (1 file is also acceptable).
- As we are not running `mypy` in our CI tests, the user who is submitting a pull request should run it on their local machine and ensure there are no errors in their submission.
- Please ensure your pull request title contains the word `mypy` in it. If possible use this template for your pull request title:
```
[mypy] Fix type annotations for <filenames>
```

### Which errors to fix?

Please follow the below steps to produce all the errors in this library:
- Fork this repository if you haven't already.
- Clone the forked repository on your local machine using the command:

```
git clone --depth 1 https://github.com/TheAlgorithms/Python.git
```
Then you need to install all the necessary requirements:
```
cd python/
python -m pip install --upgrade pip
python -m pip install -r requirements.txt
python -m pip install mypy
```
Then run either of the two commands:
- `mypy --ignore-missing-imports .` -> To produce all the error messages for the entire codebase.
- `mypy --ignore-missing-imports <filepath1> <filepath2> ...` -> To produce error messages for the mentioned file.

### How to fix the errors?

- Make a separate branch for your fix with the command: 
```
git checkout -b mypy-fix
```
- Make changes to the selected files.
- Push it to your forked copy and open a pull request with the appropriate title as mentioned above.

### Focus on one directory at a time:

```
.
├── [x] arithmetic_analysis
├── [x] backtracking
├── [x] bit_manipulation
├── [x] blockchain
├── [x] boolean_algebra
├── [x] cellular_automata
├── [x] ciphers
├── [x] compression
├── [x] computer_vision
├── [x] conversions
├── [ ] data_structures
├── [x] digital_image_processing
├── [x] divide_and_conquer
├── [ ] dynamic_programming
├── [x] electronics
├── [x] file_transfer
├── [x] fractals
├── [x] fuzzy_logic
├── [x] genetic_algorithm
├── [x] geodesy
├── [x] graphics
├── [ ] graphs
├── [x] hashes
├── [x] knapsack
├── [x] linear_algebra
├── [x] machine_learning
├── [ ] maths
├── [ ] matrix
├── [x] networking_flow
├── [x] neural_network
├── [ ] other
├── [ ] project_euler
├── [x] quantum
├── [x] scheduling
├── [x] scripts
├── [ ] searches
├── [x] sorts
├── [ ] strings
└── [x] web_programming
```

### Pre-requisites:
- You should be familiar with `mypy`: https://mypy.readthedocs.io
- You should be familiar with Python type hints: https://docs.python.org/3/library/typing.html


Discussion:
@dhruvmanila I am beginner programmer in python. Is there any help I can do regarding this? 
wrking

# Update:

With the latest update for `mypy` http://mypy-lang.org/, it supports [PEP 585](https://www.python.org/dev/peps/pep-0585/) which lets us use `list[int]` instead of `List[int]`. We always run on the latest Python version so we will adopt the built in generic types instead of importing it from the `typing` module.
I updated the list above to reflect the directories that pass in our build GitHub Action.  As contributors fix directories, please add them to the mypy tests in `.github/workflows/build.yml` so that they get tested and we do not have regressions.
So, here's the crux of the issue: mypy does not try type-checking every single module you've imported. Instead, it only attempts to type-check modules that have explicitly opted-in to the typing ecosystem.

Modules can opt-in to the typing ecosystem via two key mechanisms:

Add type hints or stubs to their code, and include a file named py.typed within the package they distribute to PyPi (or any other package repository). The presence of this marker makes the package PEP-561-aware. The mypy docs also have more info about PEP-561-aware packages.
Alternatively, add stubs to typeshed, the repository of type hints for the standard library and select 3rd party libraries.
The aws_xray_sdk package has done neither of these things, so will be ignored by mypy.
@ayushigoyal2840 The next step is to [remove the `exclude` statement](https://github.com/TheAlgorithms/Python/blob/master/mypy.ini#L5) while keeping the tests green.  Once that is done, we can look into the missing imports.  Once that is done, we can try adding `--strict`
Great work team
@ikobangs There is [still work to do](https://github.com/TheAlgorithms/Python/blob/master/mypy.ini#L5) so please consider attacking one of the following directories:
* [ ] data_structures #4362 
* [ ]  dynamic_programming #4332
* [ ]  graphs
* [ ]  maths #4362 #4358
* [ ]  matrix
* [ ]  other
* [ ]  project_euler
* [ ]  searches #4323 #4352
* [ ]  strings
Where to start
This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

I'm a beginner in Python, is there any help I can do?
This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

Please reopen this issue once you add more information and updates here. If this is not the case and you need some help, feel free to seek help from our [Gitter](https://gitter.im/TheAlgorithms) or ping one of the reviewers. Thank you for your contributions!

Hello... Can I help with any of the issues here? ..i want to learn the ways ...so i also might need some guidance
Hello .. Can I help with any issues here? Like if someone assigns me some work I would be grateful to work on that 
 No one assigns work.  We just review pull requests so please go ahead.
Now how to solve it 
@AminVerve14 Read all the instructions given in the guidelines of this issue, you will get to know
I have done fixes for the entire proj euler repo

its amazing project
@dhruvmanila I believe there are no remaining meaningful fixes to do, as the left ones are adressed by this

> # Update:
> With the latest update for `mypy` http://mypy-lang.org/, it supports [PEP 585](https://www.python.org/dev/peps/pep-0585/) which lets us use `list[int]` instead of `List[int]`. We always run on the latest Python version so we will adopt the built in generic types instead of importing it from the `typing` module.


> @dhruvmanila I believe there are no remaining meaningful fixes to do, as the left ones are adressed by this
> 
> > # Update:
> > With the latest update for `mypy` http://mypy-lang.org/, it supports [PEP 585](https://www.python.org/dev/peps/pep-0585/) which lets us use `list[int]` instead of `List[int]`. We always run on the latest Python version so we will adopt the built in generic types instead of importing it from the `typing` module.

Indeed when you run command `mypy --ignore-missing-imports .` it just shows those kind of errors. However, I do see some files that do not have type annotations and are not shown by that.

for example
https://github.com/TheAlgorithms/Python/blob/729b4d875a07bd15bc6e5e8a3c79f16fa1e003e6/graphs/a_star.py 

Should we be using a different command? or am I missing something?



Please add `from __future__ import annotations` and use `list`, not `List` because Python 3.10 is already released and we will move to it as soon as opencv-python gets compatible.
> > @dhruvmanila I believe there are no remaining meaningful fixes to do, as the left ones are adressed by this
> > > # Update:
> > > With the latest update for `mypy` http://mypy-lang.org/, it supports [PEP 585](https://www.python.org/dev/peps/pep-0585/) which lets us use `list[int]` instead of `List[int]`. We always run on the latest Python version so we will adopt the built in generic types instead of importing it from the `typing` module.
> 
> Indeed when you run command `mypy --ignore-missing-imports .` it just shows those kind of errors. However, I do see some files that do not have type annotations and are not shown by that.
> 
> for example https://github.com/TheAlgorithms/Python/blob/729b4d875a07bd15bc6e5e8a3c79f16fa1e003e6/graphs/a_star.py
> 
> Should we be using a different command? or am I missing something?

The reason this is passing is that we're running mypy in the loosest of settings right now. To increase the actual coverage of type annotations (and get the most benefit), we should use the `--strict` flag. That's *really* strict though, so perhaps we can go with `--disallow-untyped-defs --check-untyped-defs --disallow-untyped-decorators --strict-equality` to begin with and work our way up.

On current `master`, I get the following results:
- `mypy --disallow-untyped-defs --check-untyped-defs --disallow-untyped-decorators --strict-equality .`
  - `Found 529 errors in 139 files (checked 649 source files)`
- `mypy --strict .`
  - `Found 1165 errors in 201 files (checked 649 source files)`

Both of these are without all of the ignored directories from `mypy.ini`. Removing that exclude list leads to
- `mypy --disallow-untyped-defs --check-untyped-defs --disallow-untyped-decorators --strict-equality .`
  - `Found 1572 errors in 321 files (checked 950 source files)`
- `mypy --strict .`
  - `Found 3026 errors in 412 files (checked 950 source files)`

tl;dr: there's still lots of room for improvement here :)

Whle happily plugging away fixing mypy issues, I inadvertently triggered the bot by opening too many MRs :smile:  See https://github.com/TheAlgorithms/Python/pull/5492. I understand the need for the bot, but I was really just following the stated protocol of opening 1 MR per file. 

Shall I work by directory instead @dhruvmanila ? It'd save me considerable overhead in creating potentially many MRs, but would lead to probably considerably bigger MRs. I see that @pikulet ran into the same problem fixing the proj euler files and then switched to 1 MR for all the proj euler files.
I would be willing to live with mypy fixes on a directory-by-directory basis.

I doubt that we need to go all the way to `—strict`.  Having type hints for all function parameters and return types is super helpful but we do not want mypy wound up so tight that beginning developers cannot contribute.
Going directory by directory now: 3 additional directories done. Back into timeout, because the next PR will make the bot angry ;)

I'm personally aiming for `--strict` compliance with my contributions (to set a good example), but I agree with @cclaus that we probably don't want to enforce that level due to the chance of scaring off beginning developers. I do think we should (eventually) enforce `--disallow-untyped-defs --check-untyped-defs --disallow-untyped-decorators --strict-equality` because the first 3 in that list are the useful ones from a documentation/editor integration point of view and the last one often triggers on bugs.
When you get a chance, please open #5648, #5653, and #5656.  

I'm over my quota of open pull requests. :)
#5608 Can anyone explain why the __exclude__ in `mypy.ini` does not work?!?
What remains???  https://github.com/TheAlgorithms/Python/blob/master/mypy.ini#L5

* [x] graphs/boruvka.py
* [x] graphs/breadth_first_search.py
* [x] graphs/breadth_first_search_2.py
* [x] graphs/check_cycle.py
* [x] graphs/finding_bridges.py
* [x] graphs/greedy_min_vertex_cover.py
* [x] graphs/random_graph_generator.py
* [x] matrix_operation.py #5808
* [ ] other/least_recently_used.py
* [ ] other/lfu_cache.py
* [ ] other/lru_cache.py
* [x] searches/simulated_annealing.py #5799
* [x] searches/ternary_search.py #5799



Resolving patch:
diff --git a/other/least_recently_used.py b/other/least_recently_used.py
--- a/other/least_recently_used.py
+++ b/other/least_recently_used.py
@@ -1,5 +1,4 @@
 import sys
-from abc import abstractmethod
 from collections import deque
 
 
@@ -10,7 +9,6 @@ class LRUCache:
     key_reference_map = object()  # References of the keys in cache
     _MAX_CAPACITY: int = 10  # Maximum capacity of cache
 
-    @abstractmethod
     def __init__(self, n: int):
         """Creates an empty store and map for the keys.
         The LRUCache is set the size n.


Test patch: