Five Most Common Python Shortcuts

dictionary.py

sentence = "i like apple"
# Create a dictionary counting character frequency of ``sentence``

# With using default dicionary 
from collections import defaultdict
frequencies = defaultdict(int) 
for char in sentence:
   frequencies[char] += 1

# Without using defualt dictionary 
frequencies = {}
for char in sentence:
   if char in frequencies:
      frequencies[char] += 1
   else:
      frequencies[char] = 1

enumerate.py

import collections
people = ["James", "Messi", "James", "Ronaldo"]
peopleAppearAt = collections.defaultdict(list)
for i, name in enumerate(people):
    peopleAppearAt[name].append(i)

# Result 
peopleAppearAt : 
{ 
   "James" : [0, 2],
   "Messi" : [1],
   "Ronaldo" : [3]
}

matrix.py

# Create a 4 x 2 matrix
col = 4
row = 2
matrix = [[0]*col for _ in range(row)]

sort.py

arr = [5, 1, 3]

# Sort not in place (return a new array)
new_sorted_array = sorted(arr)

# Sort in place (return None) 
arr.sort()

sort_two.py

animal_age = [[4,"cat"], [1, "dog"], [2, "cat"]]

# Sort the list by first index or age 
# animal_age : [[1, 'dog'], [2, 'cat'], [4, 'cat']]
animal_age.sort(key = lambda x : x[0])

# Sort the list by second index or name of animals
# animal_age : [[2, 'cat'], [4, 'cat'], [1, 'dog']]
animal_age.sort(key = lambda x : x[1])

# Sort the list by both attributes by comparing the name first
# if tie, compare the age from old to young(descendingly)
# animal_age = [[4, 'cat'], [2, 'cat'], [1, 'dog']]

animal_age.sort(key = lambda x: (x[1], -x[0]))

ternary.py

# Format of Python Ternary
""" 
value = value_when_true if condition else value_when_false
"""

# Example
x = 5
equal_five = True if x == 5 else False