Python3 Pro Tips Cheat Sheet by eazykaye

# initializing
d1 = { 'k1': 'v1', 'k2': 'v2' }
d2 = dict(k3='v3', k4='v4')

# merging
d3 = d1|d2  # python3.9  or later
d3 = { **d1, **d2 }

# comprehension syntax
d4 = { i:'static_value' for i in some_list }

# iterating
for k,v in d1.items():
    print(f"Key {k} has a value of {v}")

s1 = {1,2,3}
s2 = {3,4,5}
s3 = {5,6,7}

s1.intersection(s2)
# {3}

s1.union(s2)
# {1, 2, 3, 4, 5}

s1.union(s2, s3)
# {1, 2, 3, 4, 5, 6, 7}

# ternary operators
x = 'foo' if 2+2==5 else 'bar'  # x = 'bar'

## 'sep' argument ##
print(1, 2, 3, sep="\n")
# 1
# 2
# 3

## end argument ##
print('address', end='@')
print('domain[.]com')
# address@domain[.]com

## repeat printing ##
print("Python" * 3)
# PythonPythonPython

import argparse

parser = argparse.ArgumentParser()
parser.add_argument('-c', '--count', type=int, required=True)
parser.add_argument('-o', '--operator', choices=['add', 'subtract'])
parser.add_argument('-n', '--number', dest='alternate_variable_name')
parser.add_argument('-v', '--verbose', action='store_true', help='enable verbose output')
args = parser.parse_args()

print(args.count)
print(args.alternate_variable_name)

from dataclasses import dataclass

@dataclass
class Person():
    name: str
    age: int
    employed: bool

    def __repr__(self):
        return f"Name: {self.name}, Age: {self.age}, Employed: {self.employed}"

class Car:
    def __init__(self, make, model):
        self.make = make
        self.model = model

    def OtherFunction(self):
        pass

"AAABBCCCC".count('C')  # 4
"AAABBCCCC".index('B')  # 3

"   strip both sides   ".strip()  # 'strip both sides'
"   strip left side   ".lstrip()  # 'strip left side   '
"   strip right side   ".rstrip()  # '   strip right side'

",".join(['list', 'of', 'words', 'to', 'join'])  # "list, of, words, to, join"

# merge lists
list3 = list1 + list2

# basic list comprehension
# syntax: [exp for member in iterable (if conditional)]
[x for x in range(10) if x > 5]  # [6, 7, 8, 9]

# nested list comprehension
[f"{x}{y}" for x in "ab" for y in "cd"]  # ['ac', 'ad', 'bc', 'bd']

# slicing  |  syntax: List[ Start Index : End Index(not inclusive) : Step ]
L1 = [0,1,2,3,4,5,6,7,8,9]
L1[4:7]  # [4, 5, 6]
L1[::2]  # [0, 2, 4, 6, 8]
L1[::-1]  # [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]

# unpacking
first, *middle, last = [0,1,2,3,4,5,6,7,8,9]
  # first = 0
  # middle = [1, 2, 3, 4, 5, 6, 7, 8]
  # last = 9

# zip
a = [1, 2, 3]
b = [4, 5, 6]
z = zip(a, b)
list(z)
# [(1, 4), (2, 5), (3, 6)]

round(5.2)  # 5
round(5.7)  # 6

from math import floor, ceil
floor(5.2)  # 5
ceil(5.2)  # 6

abs(-5.2)  # 5.2
min([1,2,3])  # 1
max([1,2,3])  # 3
sum([1,2,3])  # 6

#eval()

exp = "2 + 2"
eval(exp)  # 4

exp = "+".join([str(n) for n in range(9)])
print(exp)  #  '0+1+2+3+4+5+6+7+8'
eval(exp)  # 36

all([ 2 > 1, 3 > 2, 4 > 5 ])
# False

any([ 2 > 1, 3 > 2, 4 > 5 ])
# True

import logging
from logging.handlers import RotatingFileHandler, TimedRotatingFileHandler

logger = logging.getLogger("logger_name")
logger.setLevel(logging.DEBUG)
fmtr = logging.Formatter('%(asctime)s - %(levelname)s - [line %(lineno)s] - %(message)s')
logfile = '/path/to/log/file'

fh = TimedRotatingFileHandler(logfile, when='midnight', interval=1, backupCount=30)
fh.setFormatter(fmtr)
fh.setLevel(logging.DEBUG)
logger.addHandler(fh)

ch = logging.StreamHandler()
ch.setFormatter(fmtr)
ch.setLevel(logging.DEBUG)
logger.addHandler(cd)

try:
    # code here
except Exception as e:
    logger.critical("Exception running that code!")
    logger.critical(e, exc_info=True)
else:
    #runs if no exceptions were raised
finally
    #always runs, good for closing resources and such

import os, glob

# concatenate file paths
filepath = os.path.join('/tmp/', 'subdir', 'filename.txt')  # '/tmp/subdir/filename.txt'

# read in files using context manager
with open(filepath, 'r') as f:
    file_contents = f.readlines()