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https://core-electronics.com.au/guides/python-reference-cheat-sheet/

Installation

For Arch Linux, install python and python-pip from the Arch repository using either yay or pacman.

yay python
yay python-pip

For dependency isolation, most Pythons packaged with Linux requires running in a virtual environment.

python -m venv /home/mtan/Source/project-name
/home/mtan/Source/project-name/bin/python
/home/mtna/Source/project-name/bin/pip

Packages

Python's package manager is pip. Here are some basic commands.

pip install <package name>
pip uninstall <package name>
pip install <package name> --upgrade
pip install <package name> --U

Import

import time
import math from sqrt
import sendmail from emailer // email
import requests // http
import csv // csv files
import os // file system
import matplotlib.pyplot as plt // charts

Command Line Arguments

Basic

import sys

file_name = sys.argv[0]
num_arguments = len(sys.argv)
arguments = sys.arv[1]

Validate Arguments

import sys
import os

# Validate CLI arguments
if len(sys.argv) == 1 or len(sys.argv) > 3:
    print('app_name: bad usage')
    print('')
    print('Usage:')
    print(' python3 app_name.py <file> <device> [options]')
    print(' python3 app_name.py file.txt D1232AC -f')
    print('')
    print('Converts a debug log file into a human-readible time sequence')
    print('')
    print('Options:')
    print(' -f, --fast       Faster parsing with less data output')
    print('')
    exit(1)

# Process CLI argument for file name
if not os.path.isfile(sys.argv[1]):
    print('Error: File "' + sys.argv[1] + '" not found')
    print('')
    exit(1)
else:
    file_name = sys.argv[1]


# Process CLI argument for options
if len(sys.argv) == 3 and (sys.argv[2] == '-f' or sys.argv[2] == '--fast'):
    fast_option = True
else:
    print('Error: Invalid option "' + sys.argv[2])
    print('')
    exit(1)

Execution Interruptors

# Exit without errors
exit(0)

# Exit with errors
exit(1)

# Exit loop/iterator
break

Naming Conventions

my_variable_name
my_function_name

Data Types

Number

5

String

'I am a string'  
"I am a string"

Boolean

True
False

Collections

There are 4 data types used to store multiple items as a collection of data: List, Tuple, Dictionary, and Set.

Type Ordered? Changeable? Allow Duplicate? Indexed?
List Yes Yes Yes Yes
Tuple Yes No Yes Yes
Dictionary Yes Yes No No (key only)
Set No No No No (iterator only)

List

["apple", "banana", "cherry"]

Tuple

("apple", "banana", "cherry")

Dictionary

{ "id" : "1234-ABCD", "firstName" : "john" , "lastName" : "smith" }

Set

{"apple", "banana", "cherry"}

Variables

x = 5
x = 'I am a string now'
x = "I am also a string"

Operators

1+3
1*3
2**3 // integer operation
2//3 // integer operation
1-3
1/3
2%3
x > y
x < y
x <= y
x >= y
x == y
x != y
x | y
x & y
not True
not False

Conditions & Loops

If-Else If-Else

if():
  // code
elif():
  // code
else:
  // code

For Loop

for i in range(1,10):
  print(i)
  
for i in myList:
  print(i)

While Loop

while (i < 9):
  print(i)
  break

Functions

Definition

def functionName(parameter):
  return (parameter)

Lambda Function

Basically an arrow function in JavaScript.

return = lambda a : a + 1

Classes

class myClass:
  def __init__(self, x, y):
    self.input1 = x
    self.input2 = y
  def myClassMethod(self):
    return self.input1 + self.input2

Samples

HTTP Get

r = requests.get(i_file_url, auth=(USERNAME,PASSWORD))

File Handling

File Size

Method 1 - Fastest

import os
return os.stat("file.txt").st_size

Method 2

import os
os.path.getsize("file.txt")

Read a File

Method 1 - Read & Print

with open(os.getcwd() + '/input-jira.csv', 'wb') as f: f.write(r.content)

Method 2 - Read & Print Line-by-Line

file = open('file_to_open.txt', 'r')
lines = file.read().splitlines()
file.close()

for line in lines:
  # Do something with the line

Method 3 - Read as CSV File

with open('input-jira.csv', newline='') as csv_file:
  csv_file = csv.reader(csv_file, delimiter=',')
  for x in csv_file: jira_list.append(x) #Create a list object.

Method 4 - Use DictReader Object

csv_records = []
csv_file = csv.DictReader(open('file.csv', 'r')) # Open CSV file as read-only and create a DictReader object.
for col in csv_file:
    csv_records.append(col['column_name'])
print(csv_records)

Write a File

with open(OUTPUT_CSV, mode='w') as export_file:
  file_writer = csv.writer(export_file, delimiter=',',quotechar='"', quoting=csv.QUOTE_MINIMAL)
  file_writer.writerow(["Sprint Name", "Planned Points", "Finished Points", "Remaining Points"])
  for x in sprint_summary:
    file_writer.writerow(x)

Plot a Chart

plt.figure(figsize=(12,6))
plt.title(i_title)
plt.xlabel("Sprint/Finish Date")
plt.ylabel("Story Points")
plt.bar(x_sprints, y_remaining, color = '#587CA1', label="Remaining")
plt.bar(x_sprints, y_finished, color = '#E3ECB8', bottom = y_remaining, label="Finished")
plt.legend()
plt.savefig(OUTPUT_PNG)