Python Cheat Sheet Part - 4
Tags: beginners, programming, tutorial, python
Published: 2022-05-05 17:33:38

**File Handling**
File handling refers to reading or writing data from files. Python provides some functions that allow us to manipulate data in the files.

**open() function**

```
var_name = open("file name", "opening mode")
```
**close() function**

```
var_name.close()
```
**read () function**
The read functions contains different methods, read(),readline() and readlines()

```
read() #return one big string
```
It returns a list of lines

```
readlines() #returns a list
```
It returns one line at a time

```
readline #returns one line at a time
```
**write function**
This function writes a sequence of strings to the file.

```
write() #Used to write a fixed sequence of characters to a file
```
It is used to write a list of strings

```
writelines()
```
**append() function**
The append function is used to append to the file instead of overwriting it. To append to an existing file, simply open the file in append mode by using 'a' as the second argument of open() as follows:

```
file = open("Hello.txt", "a")
```

**Exception Handling**
An exception is an unusual condition that results in an interruption in the flow of a program.

**try and except**
A basic try-catch block in python. When the try block throws an error, the control goes to the except block.

```
try:
    [Statement body block]
    raise Exception()
except Exception as e:
    [Error processing block]
```

**Object Oriented Programming (OOPS)**
It is a programming approach that primarily focuses on using objects and classes. The objects can be any real-world entities.

**class**
The syntax for writing a class in python

```
class class_name:
    pass #statements
```
**class with a constructor**
The syntax for writing a class with the constructor in python

```
class Example:

    # Default constructor
    def __init__(self):
        self.name = "Example"

    # A method for printing data members
    def print_me(self):
        print(self.name)
```
**Creating an object**
Instantiating an object can be done as follows:

```
<object-name> = <class-name>(<arguments>)
```
**filter function**
The filter function allows you to process an iterable and extract those items that satisfy a given condition

```
filter(function, iterable)
```
**issubclass function**
Used to find whether a class is a subclass of a given class or not as follows

```
issubclass(obj, classinfo) # returns true if obj is a subclass of classinfo
```
**Iterators and Generators**
Here are some of the advanced topics of the Python programming language like iterators and generators

**Iterator**
Used to create an iterator over an iterable

```
iter_list = iter(['Harry', 'Aakash', 'Rohan']) 
print(next(iter_list)) 
print(next(iter_list)) 
print(next(iter_list))
```
**Generator**
Used to generate values on the fly

```
# A simple generator function
def my_gen():
    n = 1
    print('This is printed first')
    # Generator function contains yield statements
    yield n
    n += 1
    print('This is printed second')
    yield n
    n += 1
    print('This is printed at last')
    yield n
```
**Decorators**
Decorators are used to modifying the behavior of a function or a class. They are usually called before the definition of a function you want to decorate.

**property Decorator (getter)**

```
@property
def name(self):
    return self.__name
```
**setter Decorator**
It is used to set the property 'name'

```
@name.setter
def name(self, value):
    self.__name=value
```
**deleter Decorator**
It is used to delete the property 'name'

@name.deleter #property-name.deleter decorator

```
def name(self, value):
    print('Deleting..')
    del self.__name
```
[Python cheat sheet part-1](https://dev.to/sandeepk27/python-cheat-sheet-for-beginners-part-1-5baj)


[Python cheat sheet part-2](https://dev.to/sandeepk27/python-cheat-sheet-part-2-5cc3)


[Python cheat sheet part-3](https://dev.to/sandeepk27/python-cheat-sheet-part-3-2mjg)