Python for JS dev

This cheatsheet is focused more on discrepancies between languages. I.e. you won't find explanation of e.g. * (multiplication) operator as it has exactly same semantics in both languages.

Explanations are given as code examples.

The cheatsheet is also structured rather in a way 'how to read Python code' than 'how to translate some JS into Python'.

Operation	Python	Better Python	JavaScript
Basics
Inline comment	`# comment`		`// comment`
Docstring	`''' Function single docstring, make sure to indent '''`	`"""`	`/**`
		`Miltiline docstring after fn definition.`	`Multiline JSDoc string.`
		`Make sure to indent as fn body code`	`Normally aligned with fn definition line`
		`"""`	`*/`
Integer division	`-8//5 == -2`		`Math.floor(a/b)`
String concat	`+`	space	`'A' 'b' == 'Ab'`
Template string	`'{} {} {}'.format(name, age, age*12)`	`f'{name} {age} {age*12}'`	`${name} ${age} ${age*12}`
No op when any statement required	`pass`		`{ } // empty block`
Map array	`dest = [x*2 for x in source]`		`const dest = source.map(x => x * 2)`
Map array	`dest = [x2 if x % 2 else x 3 for x in source]`		`const dest = source.map(x => x % 2 ? x * 2 : x * 3)`
Filter array	`dest = [x if x % 2 for x in source]`		`const dest = source.filter(x => x % 2)`
Filter/map array	`dest = [x*2 if x % 2 for x in source]`		`const dest = source.filter(x => x % 2).map(x => x * 2)`
Exceptions handling	`try: except Exception as e: else: finally:`		`try {} catch(e) {} finally {} // no 'else' block substitution`
Exception invocation	`raise`		`throw new Exception()`

Iterators

sq_list = [x**2 for x in range(10)]  # this produces a list of squares
sq_iterator = (x**2 for x in range(10))  # this produces an iterator of squares

Working with files

with open(file_path, rw_options) as f:
    file_data = f.read(bytes_to_read) # or readline()
    # f.close() is done automatically
    
lines = []
with open(file_path, rw_options) as f:
    for line in f:
        lines.append(line.strip())

Modules

if __name__ == "__main__":
    main()
    
def main():
    # executable code, e.g. tests

import module as m
import module.submodule
from module import object1, object2
from module import object1 as o1
from module import * # anti-pattern

Libraries

See https://pymotw.com/3/

csv: very convenient for reading and writing csv files
collections: useful extensions of the usual data types including OrderedDict, defaultdict and namedtuple
random: generates pseudo-random numbers, shuffles sequences randomly and chooses random items
string: more functions on strings. This module also contains useful collections of letters like string.digits (a string containing all characters which are valid digits).
re: pattern-matching in strings via regular expressions
math: some standard mathematical functions
os: interacting with operating systems
os.path: submodule of os for manipulating path names
sys: work directly with the Python interpreter
json: good for reading and writing json files (good for web work)
IPython - A better interactive Python interpreter
requests - Provides easy to use methods to make web requests. Useful for accessing web APIs.
Flask - a lightweight framework for making web applications and APIs.
Django - A more featureful framework for making web applications. Django is particularly good for designing complex, content heavy, web applications.
Beautiful Soup - Used to parse HTML and extract information from it. Great for web scraping.
pytest - extends Python's builtin assertions and unittest module.
PyYAML - For reading and writing YAML files.
NumPy - The fundamental package for scientific computing with Python. It contains among other things a powerful N-dimensional array object and useful linear algebra capabilities.
pandas - A library containing high-performance, data structures and data analysis tools. In particular, pandas provides dataframes!
matplotlib - a 2D plotting library which produces publication quality figures in a variety of hardcopy formats and interactive environments.
ggplot - Another 2D plotting library, based on R's ggplot2 library.
Pillow - The Python Imaging Library adds image processing capabilities to your Python interpreter.
pyglet - A cross-platform application framework intended for game development.
Pygame - A set of Python modules designed for writing games.
pytz - World Timezone Definitions for Python

OleksiyRudenko/install-py.md

Python Dev Env

Iterators

Working with files

Modules

Libraries