Python Cheatsheet

Python is an interpreted, object-oriented, high-level programming language with dynamic semantics. Its high-level built in data structures, combined with dynamic typing and dynamic binding, make it very attractive for Rapid Application Development, as well as for use as a scripting or glue language to connect existing components together.

Basics

display

print("hello world")
Code language: Python (python)

comments

• # is used to comment a line in Python

Data Types

Category	Data Type
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

Data casting

Constructor function	desc
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

Variables

In Python, declaring variables is not required. Means you don’t need to specify whether it is an integer or string etc as Python is a dynamically typed language.

Operators

Type	Operators
Arithmetic Operators	+ – * / % ** //
Comparision 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):
       statement(s)
       #here parameters are optional
       #code

function-name(parameters)
 #calling a function
Code language: Python (python)

Example

def my_func():
	x = 10
	print("Value inside function:",x)

x = 20
my_func()
print("Value outside function:",x)
Code language: PHP (php)

Collections

1. List

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

Example

mylist=["iPhone","Pixel","Samsung"]
print(mylist[0]) # prints iPhone
print(mylist[7]) # throws IndexError : list index out of range
print(mylist[-1]) # prints Samsung
Code language: Python (python)

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.

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
Code language: Python (python)

3. Set

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

Example

mySet = {"iPhone", "Pixel", "Samsung"}
mySet.add('OnePlus')
print(mySet) # prints {'iPhone', 'Samsung', 'OnePlus', 'Pixel'}
Code language: Python (python)

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.

Example

mydict = {
    "brand" :"iPhone",
    "model": "iPhone 11"
}
val = mydict["brand"]
print(val) # prints iPhone
Code language: Python (python)

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()	To 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
Code language: Python (python)

2. If-else

if conditional-expression :
    #code
else :
    #code
Code language: Python (python)

3. Nested-If-else

if conditional-expression :
    #code
elif conditional-expression :
    #code
else :
    #code
Code language: Python (python)

Loops

1. For

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

Syntax

for variable in arrays :
    #code
Code language: CSS (css)

2. While

while condition  
    #code 
Code language: PHP (php)

Useful 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()

Python with Mongodb

Install a python driver pymongo to connect with MongoDB.

Create Database

import pymongo

db = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = db["sample"]
Code language: Python (python)

Create collection

import pymongo
db = pymongo.MongoClient("mongodb://localhost:27017/")
mydb = db["sample"]

mycln = mydb["details"]
Code language: Python (python)

Insert

<em>#insert a single document</em>
doc = mycln.insert_one(mydict)
# insert multiple documents
mylist =[
    {"name": "foo", "age": 20},
    {"name": "bar", "age": 25},
    {"name": "apple", "age": 30}
]
doc1 = mycln.insert_many(mylist)
Code language: Python (python)

Read

#to return all the documents
<strong>for</strong> doc <strong>in</strong> mycln.find():
  print(doc)

# to return first occurence
doc1=mycln.find_one()
print(doc1)
Code language: Python (python)

Update

# to update a single document
mycln.update_one({"name" : "foo"}, {"$set":{"age": 23}})
Code language: Python (python)

Delete

# to delete a single document
doc1 = mycln.delete_one({"name" : "foo"})
Code language: Python (python)

Python with Files

Create

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

file = open("myfile.txt","c")
Code language: Python (python)

Read

Use open() function with r as mode.

file = open("myfile.txt","r")
print(file.read())
Code language: Python (python)

Update or Append

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

file = open("myfile.txt","a")
file.write("Happy learning!!")
file.close()
Code language: Python (python)

Delete

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

import os
os.remove(filename)
Code language: Python (python)

If you have quires and suggestions put them in the comments.Hope this Python Cheatsheet useful to you, Share & Help Other to learn 🙂