python.md

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)