Python Cheatsheet Cheatsheet




Basics

display

print("hello world")

comments

  • # is used to comment a line in Python

Data Types

CategoryData Type
Textstr
Numberint, float, complex
Booleanbool
Binarybytes, bytearray, memoryview
Setset, frozenset
Sequencelist, tuple, range
Mappingdict
  • type() is used to know the data type of a variable

Data casting

Constructor functiondesc
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

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

Functions

# declaring a function
def function-name(parameters){ # here 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.

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

Operations

OperationDescription
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])→valueremove & 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

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'}

Operations

MethodDescriptionUsage
add()to add an element to the setmySet.add('value')
clear()to remove all the elements from the setmySet.clear()
pop()to remove last element from the setmySet.pop()
remove()to remove a specified element from the setmySet.remove("value")
del()to delete a setdel myset
copy()to return a copy of the setcopySet = mySet.copy()
union()to return a set containing the union of setsmySet3 = mySet1.union(mySet2)
update()to update the set with the union of this set and othersmySet1.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
OperationDescription
d[key]=valueTo 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()
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. Nested-If-else

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 

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 concatenationstr.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"]

Create collection

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

mycln = mydb["details"]

Insert

#insert a single document
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)

Read

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

# to return first occurence
doc1=mycln.find_one()
print(doc1)

Update

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

Delete

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

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)


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