The Ultimate Python CheatSheet
Basics Basic syntax from the python programming language
Showing Output To User the print function is used to display or print output
print("Content that you wanna print on screen")
Taking Input From User the input function is used to take input from the user
var1 = input("Enter your name: ")
Empty List This method allows you to create an empty list
my_list = []
Empty Dictionary By putting two curly braces, you can create a blank dictionary
my_dict = {}
Range Function range function returns a sequence of numbers, eg, numbers starting from 0 to n-1 for range(0, n)
range(int_value)
Comments Comments are used to make the code more understandable for programmers, and they are not executed by compiler or interpreter.
Single line comment
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#This is a single line comment
Multi-line comment
'''This is a
multi-line
comment'''
Escape Sequence An escape sequence is a sequence of characters; it doesn't represent itself when used inside string literal or character.
Newline Newline Character
\n
Backslash It adds a backslash
\\
Single Quote It adds a single quotation mark
\'
Tab It gives a tab space
\t
Backspace It adds a backspace
\b
Octal value It represents the value of an octal number
\ooo
Hex value It represents the value of a hex number
\xhh
Carriage Return Carriage return or \r is a unique feature of Python. \r will just work as you have shifted your cursor to the beginning of the string or line.
\r
Strings Python string is a sequence of characters, and each character can be individually accessed. Using its index.
String You can create Strings by enclosing text in both forms of quotes - single quotes or double-quotes.
variable_name = "String Data"
Slicing Slicing refers to obtaining a sub-string from the given string.
var_name[n : m]
String Methods isalnum() method Returns True if all characters in the string are alphanumeric
string_variable.isalnum()
isalpha() method Returns True if all characters in the string are alphabet
string_variable.isalpha()
isdecimal() method Returns True if all characters in the string are decimals
string_variable.isdecimal()
isdigit() method Returns True if all characters in the string are digits
string_variable.isdigit()
islower() method Returns True if all characters in the string are lower case
string_variable.islower()
isspace() method Returns True if all characters in the string are whitespaces
string_variable.isspace()
isupper() method Returns True if all characters in the string are upper case
string_variable.isupper()
lower() method Converts a string into lower case
string_variable.lower()
upper() method Converts a string into upper case
string_variable.upper()
strip() method It removes leading and trailing spaces in the string
string_variable.strip()
List A List in Python represents a list of comma-separated values of any data type between square brackets.
List
var_name = [element1, element2, and so on]
List Methods index method Returns the index of the first element with the specified value
list.index(element)
append method Adds an element at the end of the list
list.append(element)
extend method Add the elements of a list (or any iterable) to the end of the current list
list.extend(iterable)
insert method Adds an element at the specified position
list.insert(position, element)
pop method Removes the element at the specified position and returns it
list.pop(position)
remove method The remove( ) method removes the first occurrence of a given item from the list
list.remove(element)
clear method Removes all the elements from the list
list.clear()
count method Returns the number of elements with the specified value
list.count(value)
reverse method Reverse the order of the list
list.reverse()
sort method Sorts the list
list.sort(reverse=True|False)
Tuples Tuples are represented as a list of comma-separated values of any data type within parentheses.
Tuple Creation
variable_name = (element1, element2, ...)
Tuple Methods count method It returns the number of times a specified value occurs in a tuple
tuple.count(value)
index method It searches the tuple for a specified value and returns the position.
tuple.index(value)
Sets A set is a collection of multiple values which is both unordered and unindexed. It is written in curly brackets.
Set Creation: Way 1
var_name = {element1, element2, ...}
Set Creation: Way 2
var_name = set([element1, element2, ...])
Set Methods: add() method Adds an element to a set
set.add(element)
clear() method Remove all elements from a set
set.clear()
discard() method Removes the specified item from the set
set.discard(value)
intersection() method Returns intersection of two or more sets
set.intersection(set1, set2 ... etc)
issubset() method Checks if a Set is Subset of Another Set
set.issubset(set)
pop() method Removes an element from the set
set.pop()
remove() method Removes the specified element from the Set
set.remove(item)
union() method Returns the union of Sets
set.union(set1, set2...)
Dictionaries The dictionary is an unordered set of comma-separated key: value pairs, within {}, with the requirement that within a dictionary, no two keys can be the same.
Dictionary
<dictionary-name> = {<key>: value, <key>: value ...}
Adding Element to a dictionary By this method, one can add new elements to the dictionary
<dictionary>[<key>] = <value>
Updating Element in a dictionary If the specified key already exists, then its value will get updated
<dictionary>[<key>] = <value>
Deleting Element from a dictionary del let to delete specified key: value pair from the dictionary
del <dictionary>[<key>]
Dictionary Functions & Methods len() method It returns the length of the dictionary, i.e., the count of elements (key: value pairs) in the dictionary
len(dictionary)
clear() method Removes all the elements from the dictionary
dictionary.clear()
get() method Returns the value of the specified key
dictionary.get(keyname)
items() method Returns a list containing a tuple for each key-value pair
dictionary.items()
keys() method Returns a list containing the dictionary's keys
dictionary.keys()
values() method Returns a list of all the values in the dictionary
dictionary.values()
update() method Updates the dictionary with the specified key-value pairs
dictionary.update(iterable)
Conditional Statements The if statements are the conditional statements in Python, and these implement selection constructs (decision constructs).
if Statement
if(conditional expression):
statements
if-else Statement
if(conditional expression):
statements
else:
statements
if-elif Statement
if (conditional expression) :
statements
elif (conditional expression) :
statements
else :
statements
Nested if-else Statement
if (conditional expression):
statements
else:
statements
else:
statements
Iterative Statements An iteration statement, or loop, repeatedly executes a statement, known as the loop body, until the controlling expression is false (0).
For Loop The for loop of Python is designed to process the items of any sequence, such as a list or a string, one by one.
for <variable> in <sequence>:
statements_to_repeat
While Loop A while loop is a conditional loop that will repeat the instructions within itself as long as a conditional remains true.
while <logical-expression> :
loop-body
Break Statement The break statement enables a program to skip over a part of the code. A break statement terminates the very loop it lies within.
for <var> in <sequence> :
statement1
if <condition> :
break
statement2
statement_after_loop
Continue Statement The continue statement skips the rest of the loop statements and causes the next iteration to occur.
for <var> in <sequence> :
statement1
if <condition> :
continue
statement2
statement3
statement4
Functions A function is a block of code that performs a specific task. You can pass parameters into a function. It helps us to make our code more organized and manageable.
Function Definition
def my_function(parameters):
# Statements
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
read-lines
It returns one line at a time
readline
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 (a):
file = open("Hello.txt", "a")
Exception Handling An exception is an unusual condition that results in an interruption in the flow of the 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]
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:
#Statements
class with a constructor The syntax for writing a class with the constructor in python
class Abhiraj:
# Default constructor
def __init__(self):
self.name = "Abhiraj"
# A method for printing data members
def print_me(self):
print(self.name)
object Instantiating an object
<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 (classinfo) or not
issubclass(class, 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 function or 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
Deletor Decorator It is used to delete the property 'name'
@name.deleter #property-name.deleter decorator
def name(self, value):
print('Deleting..')
del self.__name
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