The Python Commands Cheat Sheet for Budding Programmers

print()

Display the result of a command

x=”Hello world” print(x) output: Hello world

input()

Collect inputs from users

print(input(“what is your name?”)) output: what is your name?

type()

Find the type of a variable

x=”Regular expressions” type(x) output:

len()

Find the number of items in a variable

len([1, 2, 3]) output: 3

\

Escape a character that changes the intent of a line of code

print(“I want you to add\”\””) output: I want you to add””

\n

Break a string character to start on the next line

print(“This is a line \n This is a second line”) output: This is a line This is a second line

def function_name(parameter): commands

Initiate a function with an optional parameter

def yourName(x): print(x+1)

lambda

Call an anonymous function

add_3_to = lambda y: y+3 print(add_3_to(4)) output: 7

return

Return a result from a function

def yourName(x): return x+1

class

Create a Python object

class myClass: def myFunc(x):

def __init__

Initialize the attrributes of a class

class myClass: def __init__(self, attributes…)

“__init__.py

Save a file containing a module so that it’s read successfully in another Python file

Rename a file containing a module as: “__init__.py

int()

Convert a variable to integer

int(1.234) output: 1

str()

Convert a variable to string

str(1.234) output: ‘1.234’

float()

Convert a variable to float

float(23) output: 23.0

dict(Counter())

Convert a list or a tupple into a dictionary after sorting with a Python built-in Counter

from collections import Counter dict(Counter([1,1,2,1,2,3,3,4])) output: {1: 3, 2: 2, 3: 2, 4: 1}

round()

Round up the output of an operation to the nearest whole number

round(23.445) output: 23

round(operation or number, decimal places)

Round up the output of an operation to a specific number of decimal places

round(23.4568, 2) output: 23.46

if:

Initiate a conditional statement

if 2<3: print(“Two is smaller”)

elif:

Make a counterstatement when the if statement is False

if 2<3: print(“Two is smaller”) elif 2==3: print(“Go on”)

else:

Make a final counterstatement if other conditions are False

if 2<3: print(“Two is smaller”) elif 2==3: print(“Go on”) else: print(“Three is greater”)

continue

Ignore a condition and execute the rest of the loop

a=[1, 4, -10, 6, 8] for b in a: if b<=0: continue print(b) output: 1 4 6 8

break

Terminate the flow of a loop with a given condition

a=[1, 4, -10, 6, 8] for b in a: if b>=6: break print(b) output: 1 4 -10

pass

Ignore a set of prior instructions

for b in a: pass

try, except

Try a block of code, else, raise a defined exception

try: print(a) except: print(“An error occured!”) output: An error occured!

finally

Execute a final code when the try and the except blocks fail

try: print(a) except: print(d) finally: print(“You can’t print an undefined variable”) output: You can’t print an undefined variable

raise Exception()

Raise an exception that stops the command when execution isn’t possible

a=7+2 if a<10: raise Exception(“Oh! You didn’t get a score of 10”)

import x

Import a whole module or library

import math

from x import y

Import a library x from a file, or a class y

from scipy.stats import mode

as

Customize an expression to your preferred name

import pandas as pd

in

Check if a value is present in a variable

x=[1, 4, 6, 7] if 5 in x: print(“There is a five”) else: print(“There is no five”) output: There is no five

is

Check if two variables refer to a single element

x=[1, 4, 6, 7] x=b print(x is b) True

None

Declare a null value

x=None

<

Check if one value is lesser than another

5<10 output: True

>

Check if one value is more than another

5>10 output: False

<=

Check if a value is lesser or equal to another

2*2<=3 output: False

>=

Check if a value is greater or equal to another

2*2>=3 output: True

“==

Check if a value is exactly equal to the other

3==4 ouput: False

!=

Ascertain that a value is not equal to the other

3!=4 ouput: True

import re

Import Python’s built-in regular expressions

import re re.findall(“strings”, variable)

a|b

Check if either of two elements are present in a string

import re someText=”Hello regular expression” a=re.findall(“regular|Hello”, someText) print(a) output: [‘Hello’, ‘regular’]

string$

Check if a variable ends with a set of strings

import re someText=”Hello regular expression” a=re.findall(“expression$”, someText) output: [‘expression’]

^string

Check if a variable starts with a set of strings

import re someText=”Hello regular expression” a=re.findall(“^Hello”, someText) print(a) output: [‘Hello’]

string.index()

Check the index position of a string character

a= “Hello World” a.index(‘H’) output: 0

string.capitalize()

Capitalize the first character in a set of strings

a= “Hello World” a.capitalize() output: ‘Hello world’

string.swapcase()

Print the first letter of each word as a lower case and the others as upper case

a= “Hello World” a.swapcase() output: ‘hELLO wORLD’

string.lower()

Convert all the strings to a lowercase

a= “Hello World” a.lower() output: ‘hello world’

string.upper()

Convert all strings to uppercase

a= “Hello World” a.upper() output: ‘HELLO WORLD’

string.startswith()

Check if a string starts with a particular character

a= “Hello World” a.startswith(‘a’) output: False

string.endswith()

Check if a string ends with a particular character

a= “Hello World” a.endswith(‘d’) output: True

string.split()

Separate each word into a list

a= “Hello World” a.split() output: [‘Hello’, ‘world’]

strings {}’.format()

Display an output as string

a=3+4 print(“The answer is {}”.format(a)) output: The answer is 7

is not None

Check if the value of a variable is not empty

def checknull(a): if a is not None: return “its full!” else: return “its empty!”

x%y

Find the remainder (modulus) of a division

9%4 output: 1

x//y

Find the quotient of a division

9//4 output: 2

“=

Assign a value to a variable

a={1:5, 3:4}

“+

Add elements together

“-

Find the difference between a set of numbers

3-4 output=-1

“*

Find the product of a set of numbers

3*4 output:12

a+=x

Add x to variable a without assigning its value to a new variable

a=2 a+=3 output: 5

a-=x

Subsract x from variable a without assigning it to a new variable

a=3 a-=2 output: 1

a*=x

Find the product of variable a and x without assigning the resullt to a new variable

a=[1, 3, 4] a*=2 output: [1, 3, 4, 1, 3, 4]

x**y

Raise base x to power y

2**3 output: 8

pow(x, y)

Raise x to the power of y

pow(2, 3) output: 8

abs(x)

Convert a negative integer to its absolute value

abs(-5) output: 5

x**(1/nth)

Find the nth root of a number

8**(1/3) output: 2

a=b=c=d=x

Assign the same value to multiple variables

a=b=c=d=”Hello world”

x, y = y, x

Swap variables

x = [1, 2] y = 3 x, y = y, x print(x, y) output: 3 [1, 2]

for

Loop through the elements in a variable

a=[1, 3, 5] for b in a: print(b, “x”, “2”, “=”, b*2) output: 1 x 2 = 2 3 x 2 = 6 5 x 2 = 10

while

Keep looping through a variable, as far as a particular condition remains True

a=4 b=2 while b<=a: print(b, “is lesser than”, a) b+=1 output: 2 is lesser than 4 3 is lesser than 4 4 is lesser than 4

range()

Create a range of positive integers between x and y

x=range(4) print(x) range(0, 4) for b in x: print(b) output: 0 1 2 3

sum()

Iterate through the elements in a list

print(sum([1, 2, 3])) output:6

sum(list, start)

Return the sum of a list with an added element

print(sum([1, 2, 3], 3)) output: 9

Make a list of elements

x=[‘a’, 3, 5, ‘h’, [1, 3, 3], {‘d’:3}]

()

Create a tupple—tupples are immutable

x=(1, 2, ‘g’, 5)

{}

Create a dictionary

a={‘x’:6, ‘y’:8}

x[a:b]

Slice through a list

x=[1, 3, 5, 6] x[0:2] output: [1, 3]

x[key]

Get the value of a key in dictionary x

a={‘x’:6, ‘y’:8} print(a[‘x’]) output: 6

x.append()

Add a list of values to an empty list

x=[1] x.append([1,2,3]) print(x) output: [1, [1,2,3]]

x.extend()

Add a list of values to continue an existing list without necessarily creating a nested list

x=[1,2] x.extend([3,4,6,2]) print(x) output: [1, 2, 3, 4, 6, 2]

del(x[a:b])

Delete an item completely from a list at a specific index

x=[1,2,3,5] del(x[0:2]) print(x) output: [2,3,5]

del(x[key])

Delete a key and a value completely from a dictionary at a specific index

y={1:3, 2:5, 4:6, 8:2} del(y[1], y[8]) print(y) output= {2:5, 4:6}

dict.pop()

Pop out the value of a key and remove it from a dictionary at a specific index

a={1:3, 2:4, 5:6} a.pop(1) output: 3

dict.popitem()

Pop out the last item from a dictionary and delete it

a={1:2, 4:8, 3:5} a.popitem() output: (3, 5) print(a) output: {1:2, 4:8}

list.pop()

Pop out a given index from a list and remove it from a list

a=[1, 3, 2, 4, 1, 6, 6, 4] a.pop(-2) output: 6 print(a) output: [1, 3, 2, 4, 1, 6, 4]

clear()

Empty the elements of a list or a dictionary

x=[1, 3, 5] x.clear() print(x) output: []

remove()

Remove an item from a list

x=[1, 5, 6, 7] x.remove(1) output: [5, 6, 7]

insert()

Insert elements into a llist

x=[3, 5, 6] x.insert(1, 4) print(x) output: [1, 4, 3, 5, 6]

sort(reverse=condition)

Reverse the direction of the elements in a list

x=[1, 3, 5, 6] x.sort(reverse=True) print(x) output: [6, 5, 3, 1]

update()

Update a dictionary by changing its first element and adding any other item to its end

x={1:3, 5:6} x.update({1:4, 8:7, 4:4}) print(x) output: {1: 4, 5: 6, 8: 7, 4: 4}

keys()

Show all the keys in a dictionary

a={1:2, 4:8} a.keys() output: dict_keys([1, 4])

values()

Show all the values in a dictionary

a={1:2, 4:8} a.values() output: dict_values([2, 8])

items()

Display the keys and the values in a dictionary

a={1:2, 4:8} a.items() output: dict_items([(1, 2), (4, 8)])

get(key)

Get the value of an item in a dictionary by its key

a={1:2, 4:8, 3:5} a.get(1) output: 2

setdefault(key)

Return the original value of an element to a dictionary

a.setdefault(2)

f={**a, **b}

Merge two dictionaries

a={‘x’:6, ‘y’:8} b={‘c’:5, ‘d’:3} f={**a, **y} print(f) output:{‘x’: 6, ‘y’: 8, ‘c’: 5, ‘d’: 3}

remove()

Remove the first matching value of an element from a list without minding its index

a=[1, 3, 2, 4, 4, 1, 6, 6, 4] a.remove(4) print(a) output: [1, 3, 2, 4, 1, 6, 6, 4]

memoryview(x)

Access the internal buffers of an object

a=memoryview(object)

bytes()

Convert a memory buffer protocol into bytes

bytes(a[0:2])

bytearray()

Return an array of bytes

bytearray(object)

#

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# Python regex cheat sheet

“”” “””

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“””The Python regex cheat sheet is good for beginners It’s equally a great refresher for experts”””

Command Line

pip install package

Install an online library

pip install pandas

virtualenv name

Use virtaulenv to create a virtual environment

virtualenv myproject

mkvirtualenv name

Use virtual environment wrapper to create virtual environment

mkvirtualenv myproject

python file.py

Run the commands in a Python file

“python my_file.py

pip freeze

List out all the installed packages in a virtual environment

pip freeze

pip freeze > somefiles

Copy all installed libraries in a single file

pip freeze > requirements.txt

where

Find the installation path of Python

where python

–version

Check the version of a package

python –version

.exe

Run a Python shell

python.exe

with open(file, ‘w’)

Write to an existing file and overwrite its existing content

with open(‘regex.txt’, ‘w’) as wf: wf.write(“Hello World!”)

with open(file, ‘r’)

Open a file as read-only

with open(‘regex.txt’, ‘r’) as rf: print(rf.read()

with open(file, ‘a’)

Write to a file without overwriting its existing content

with open(‘regex.txt’, ‘a’) as af: af.write(“\nHello Yes!”)

file.close

Close a file if it’s not in use

af=open(‘regex.txt’) af.close

exit

Exit the Python shell

exit()