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PYTHON CHEATSHEET

Basics

Display

print("Hello World")

Comments

  • # is used to comment a line in Python
  • ''' ''' this is used for multiline comment in Python

Data Types

Category Data Types
Text str
Number int, float, complex
Boolean bool
Binary bytes, bytearray, memoryview
Set set, frozenset
Sequence list, tuple, range
Mapping dict
  • type() is used to know the data type of a variable

Type casting

Constructor function Description
int() constructs an integer from any form of data like string, float or integer
float() constructs a float number from any form of data like string, float or integer
str() constructs a string from any form of data like string, float or integer

Useful Math functions

Function Description
complex(x,y) Creates a complex number x+iy
chr() return a unicode string of one character
divmod(a,b) gets the quotient and remainder of a/b
ord('') return the unicode codepoint for a one character
pow(a,b) Power function ie a^b
round() Round Function
abs() Gets the absolute value

Variables

In Python, declaring variables is not required.

Operators

Type Operators
Arithmetic Operators + - * / % ** //
Relational Operators == != > >= < <=
Bitwise Operators & ^ | ^ ~ << >>
Logical Operators && || !
Assignment Operators = += -= *= /= %= **= //=
Membership Operators in, not in
Identity Operators is, is not

Functions

# declaring a function
def function-name(parameters){ # parameters are optional
    #code
}
function-name(parameters) # calling a function

Collections

1. List

List is ordered collection of items and can be changed. [] are used to represent lists. List is mutable.

Example

mylist=["Mango","Banana","Apple"]
print(mylist[1]) # prints Banana
print(mylist[7]) # throws IndexError : list index out of range
print(mylist[-3]) # prints Mango

Operations

Operation Description
lst.append(val) add an item to list at end
lst.extend(seq) add sequence of items to list at end
lst.insert(index,val) insert an item at given index
lst.remove(val) remove first item with value val
lst.pop([index])→value remove & return item at index
lst.sort() sort the given list items
lst.reverse() reverse the given list items

2. Tuple

Tuple is ordered collection of items and can't be changed. () are used to represent Tuples. Tuple is immutable.

Example

myTuple = ["iPhone","Pixel","Samsung"]
print(myTuple[0]) # prints iPhone
print(myTuple[7]) # throws IndexError: tuple index out of range
print(myTuple[-1]) # prints Samsung

3. Set

Set is unordered collection of items and it is unindexed. {} are used to represent sets. Set is mutable.

Example

mySet = {"iPhone", "Pixel", "Samsung"}
mySet.add('OnePlus')
print(mySet) # prints {'iPhone', 'Samsung', 'OnePlus', 'Pixel'}

Operations

Method Description Usage
add() to add an element to the set mySet.add('value')
clear() to remove all the elements from the set mySet.clear()
pop() to remove last element from the set mySet.pop()
remove() to remove a specified element from the set mySet.remove("value")
del() to delete a set del myset
copy() to return a copy of the set copySet = mySet.copy()
union() to return a set containing the union of sets mySet3 = mySet1.union(mySet2)
update() to update the set with the union of this set and others mySet1.update(mySet2)

4. Dictionary

Dictionary is a collection of key value pairs which is unordered, can be changed, and indexed. They are written in curly brackets with key - value pairs. Dictionary is mutable.

Example

mydict = {
    "brand" :"iPhone",
    "model": "iPhone 11"
}
val = mydict["brand"]
print(val) # prints iPhone
Operation Description
d[key]=value To add a new key-value pair to dictionary or to change it's value if key is existing
d.copy() Returns a copy of the dictionary
d.keys() Returns a list containing all the dictionary's keys
d.values() Returns a list of all the values in the dictionary
d.items() Removes the element with the specified key
d.clear() To empty the dictionary items.
del d[key] To remove an item from a dictionary.
d.pop(key) To remove an item from a dictionary.
d.popitem() removes the item that was last inserted into the dictionary
d.get(key) Returns the value of the specified key
d.setdefault(key) Returns the value of the specified key. If the key does not exist then returns the default value provided

Conditional Statements

1. If

if conditional-expression :
    #code

2. If-else

if conditional-expression :
    #code
else :
    #code

3. If-elif-else Ladder

if conditional-expression :
    #code
elif conditional-expression :
    #code
else :
    #code

Loops

1. For

For loop is used to iterate over arrays(list, tuple, set, dictionary) or strings.

Syntax

for variable in arrays :
    #code

2. While

while condition : 
    #code

String Methods
str.strip() str.lower() str.upper()
str.replace("str to be replaced","new string to replace") str.split("seperator") len(str)
+ for concatenation str.count(substr) str.find(substr)
str.index(substr, start, end) str.join(array) str.partition(substr)
str.zfill(len) str.swapcase() str.isdecimal()
str.isdigit() str.islower() str.isupper()
str.endswith(value, start, end) str.startswith(value, start, end) str.isspace()
str.isalpha() (checking for alphabets) str.isascii() (checking for ascii chars) str.title() (making each word first letter capitalized)

Python with Files

Create

Use open() function with c or a or w as mode.

file = open("myfile.txt","c")

Read

Use open() function with r as mode.

file = open("myfile.txt","r")
print(file.read())

Update or Append

Use open() function with a or w as mode.

file = open("myfile.txt","a")
file.write("Happy learning!!")
file.close()

Delete

For deleting files, you must import os module and use os.remove() function.

import os
os.remove(filename)