Python Cheatsheet

Package Management

Package management in Python helps organise collections of downloadable software packages. There are a number of package managers available, each with their own unique advantages. However, UV has become a personal favourite.

Pip

Conda

Mamba

UV

Lists

Instantiation

new_list = [value]*length

List Comprehension

new_list = [value for iteration in length]

Arrays

Arrays in Python use the numpy library.

import numpy as np

Loops

Breaking Out of Nested Loops

list1 = [1, 2, 3]
list2 = [9, 8, 7]
 
for i in list1:
	for j in list2:
		print(i, j)
		

in matrix format:

A = [[a11, a12, a13],
	[a21, a22, a23],
	[a31, a32, a33]]
 
for row in A:
	for column in row:
		print(row, column)
 

But what if we wanted to get a single element a22 from this nested list? using break inside the inner loop only stops the inner loop, at the next iteration of the outer loop, the inner loop will continue.

This is solved by

A = [[a11, a12, a13],
	[a21, a22, a23],
	[a31, a32, a33]]
	
for row in A:
	for item in row:
		if item == 'a22':
			break #breaks the inner loop
	else:
		continue # finishes the inner loop without breaking
	break
	# otherwise break the outer loop
 

Using Flags

A = [[a11, a12, a13],
	[a21, a22, a23],
	[a31, a32, a33]]
	
flag = False
for row in A:
	for item in row:
		if item == 'a22':
			flag = True
			break #breaks the inner loop
	if flag
		break
		# breaks the outer loop

Three +

 
A = [[[a111]], [a121], [a131]],
	[[a211], [a221], [a231]],
	[[a311], [a321], [a331]]]
	
flag = False
for row in A:
	for item in row:
		for cell in item
			if cell == 'a22':
				flag = True
				break #breaks the inner loop
		if flag
		break # breaks the middle loop
	if flag
		break
		# breaks the outer loop