lyrl/30-seconds-of-python

A curated collection of useful Python snippets that you can understand in 30 seconds or less.

30-seconds-of-python

Curated collection of useful Python snippets that you can understand in 30 seconds or less.

• Use Ctrl + F or command + F to search for a snippet.
• Contributions welcome, please read the contribution guide.
• If you want to follow 30-seconds-of-code on social media, you can find us on Facebook, Instagram and Twitter.

Related projects

• 30 Seconds of code
• 30 Seconds of CSS
• 30 Seconds of Interviews
• 30 Seconds of React
• 30 Seconds of PHP
• 30 Seconds of Knowledge
• 30 Seconds of Kotlin (unofficial)

Contents

List

View contents

• all_equal
• all_unique
• bifurcate
• bifurcate_by
• chunk
• compact
• count_by
• count_occurences
• deep_flatten
• difference
• difference_by
• every
• every_nth
• filter_non_unique
• group_by
• has_duplicates
• head
• initial
• initialize_2d_list
• initialize_list_with_range
• initialize_list_with_values
• intersection
• intersection_by
• last
• longest_item
• max_n
• min_n
• none
• offset
• sample
• shuffle
• similarity
• some
• spread
• symmetric_difference
• symmetric_difference_by
• tail
• union
• union_by
• unique_elements
• zip

Math

View contents

• average
• average_by
• clamp_number
• digitize
• factorial
• fibonacci
• gcd
• in_range
• is_divisible
• is_even
• is_odd
• lcm
• max_by
• min_by
• rads_to_degrees
• sum_by

Object

View contents

• keys_only
• map_values
• values_only

String

View contents

• byte_size
• camel
• capitalize
• capitalize_every_word
• decapitalize
• is_anagram
• is_lower_case
• is_upper_case
• kebab
• palindrome
• snake
• split_lines

Utility

View contents

• cast_list

---

List

all_equal

Check if all elements in a list are equal.

Use [1:] and [:-1] to compare all the values in the given list.

def all_equal(lst):
  return lst[1:] == lst[:-1]

Examples

all_equal([1, 2, 3, 4, 5, 6]) # False
all_equal([1, 1, 1, 1]) # True

⬆ Back to top

all_unique

Returns True if all the values in a flat list are unique, False otherwise.

Use set() on the given list to remove duplicates, compare its length with the length of the list.

def all_unique(lst):
  return len(lst) == len(set(lst))

Examples

x = [1,2,3,4,5,6]
y = [1,2,2,3,4,5]
all_unique(x) # True
all_unique(y) # False

⬆ Back to top

bifurcate

Splits values into two groups. If an element in filter is True, the corresponding element in the collection belongs to the first group; otherwise, it belongs to the second group.

Use list comprehension and enumerate() to add elements to groups, based on filter.

def bifurcate(lst, filter):
  return [
    [x for i,x in enumerate(lst) if filter[i] == True],
    [x for i,x in enumerate(lst) if filter[i] == False]
  ]

Examples

bifurcate(['beep', 'boop', 'foo', 'bar'], [True, True, False, True]) # [ ['beep', 'boop', 'bar'], ['foo'] ]

⬆ Back to top

bifurcate_by

Splits values into two groups according to a function, which specifies which group an element in the input list belongs to. If the function returns True, the element belongs to the first group; otherwise, it belongs to the second group.

Use list comprehension to add elements to groups, based on fn.

def bifurcate_by(lst, fn):
  return [
    [x for x in lst if fn(x)],
    [x for x in lst if not fn(x)]
  ]

Examples

bifurcate_by(['beep', 'boop', 'foo', 'bar'], lambda x: x[0] == 'b') # [ ['beep', 'boop', 'bar'], ['foo'] ]

⬆ Back to top

chunk

Chunks a list into smaller lists of a specified size.

Use list() and range() to create a list of the desired size. Use map() on the list and fill it with splices of the given list. Finally, return use created list.

from math import ceil

def chunk(lst, size):
  return list(
    map(lambda x: lst[x * size:x * size + size],
      list(range(0, ceil(len(lst) / size)))))

Examples

chunk([1,2,3,4,5],2) # [[1,2],[3,4],5]

⬆ Back to top

compact

Removes falsey values from a list.

Use filter() to filter out falsey values (False, None, 0, and "").

def compact(lst):
  return list(filter(bool, lst))

Examples

compact([0, 1, False, 2, '', 3, 'a', 's', 34]) # [ 1, 2, 3, 'a', 's', 34 ]

⬆ Back to top

count_by

Groups the elements of a list based on the given function and returns the count of elements in each group.

Use map() to map the values of the given list using the given function. Iterate over the map and increase the element count each time it occurs.

def count_by(arr, fn=lambda x: x):
  key = {}
  for el in map(fn, arr):
    key[el] = 0 if el not in key else key[el]
    key[el] += 1
  return key

Examples

from math import floor
count_by([6.1, 4.2, 6.3], floor) # {4: 1, 6: 2}
count_by(['one', 'two', 'three'], len) # {3: 2, 5: 1}

⬆ Back to top

count_occurences

Counts the occurrences of a value in a list.

Increment a counter for every item in the list that has the given value and is of the same type.

def count_occurrences(lst, val):
  return len([x for x in lst if x == val and type(x) == type(val)])

Examples

count_occurrences([1, 1, 2, 1, 2, 3], 1) # 3

⬆ Back to top

deep_flatten

Deep flattens a list.

Use recursion. Define a function, spread, that uses either list.extend() or list.append() on each element in a list to flatten it. Use list.extend() with an empty list and the spread function to flatten a list. Recursively flatten each element that is a list.

def spread(arg):
  ret = []
  for i in arg:
    if isinstance(i, list):
      ret.extend(i)
    else:
      ret.append(i)
  return ret

def deep_flatten(lst):
  result = []
  result.extend(
    spread(list(map(lambda x: deep_flatten(x) if type(x) == list else x, lst))))
  return result

Examples

deep_flatten([1, [2], [[3], 4], 5]) # [1,2,3,4,5]

⬆ Back to top

difference

Returns the difference between two iterables.

Create a set from b, then use list comprehension on a to only keep values not contained in the previously created set, _b.

def difference(a, b):
  _b = set(b)
  return [item for item in a if item not in _b]

Examples

difference([1, 2, 3], [1, 2, 4]) # [3]

⬆ Back to top

difference_by

Returns the difference between two lists, after applying the provided function to each list element of both.

Create a set by applying fn to each element in b, then use list comprehension in combination with fn on a to only keep values not contained in the previously created set, _b.

def difference_by(a, b, fn):
  _b = set(map(fn, b))
  return [item for item in a if fn(item) not in _b]

Examples

from math import floor
difference_by([2.1, 1.2], [2.3, 3.4],floor) # [1.2]
difference_by([{ 'x': 2 }, { 'x': 1 }], [{ 'x': 1 }], lambda v : v['x']) # [ { x: 2 } ]

⬆ Back to top

every

Returns True if the provided function returns True for every element in the list, False otherwise.

Iterate over the elements of the list to test if every element in the list returns True based on fn. Omit the seconds argument, fn, to check if all elements are True.

def every(lst, fn=lambda x: not not x):
  for el in lst:
    if not fn(el):
      return False
  return True

Examples

every([4, 2, 3], lambda x: x > 1) # True
every([1, 2, 3]) # True

⬆ Back to top

every_nth

Returns every nth element in a list.

Use [1::nth] to create a new list that contains every nth element of the given list.

def every_nth(lst, nth):
  return lst[1::nth]

Examples

every_nth([1, 2, 3, 4, 5, 6], 2) # [ 2, 4, 6 ]

⬆ Back to top

filter_non_unique

Filters out the non-unique values in a list.

Use list comprehension and list.count() to create a list containing only the unique values.

def filter_non_unique(lst):
  return [item for item in lst if lst.count(item) == 1]

Examples

filter_non_unique([1, 2, 2, 3, 4, 4, 5]) # [1, 3, 5]

⬆ Back to top

group_by

Groups the elements of a list based on the given function.

Use list() in combination with map() and fn to map the values of the list to the keys of an object. Use list comprehension to map each element to the appropriate key.

def group_by(lst, fn):
  groups = {}
  for key in list(map(fn,lst)):
    groups[key] = [item for item in lst if fn(item) == key]
  return groups

Examples

import math
group_by([6.1, 4.2, 6.3], math.floor); # {4: [4.2], 6: [6.1, 6.3]}
group_by(['one', 'two', 'three'], 'length'); # {3: ['one', 'two'], 5: ['three']}

⬆ Back to top

has_duplicates

Returns True if there are duplicate values in a flast list, False otherwise.

Use set() on the given list to remove duplicates, compare its length with the length of the list.

def has_duplicates(lst):
  return len(lst) != len(set(lst))

Examples

x = [1,2,3,4,5,5]
y = [1,2,3,4,5]
has_duplicates(x) # True
has_duplicates(y) # False

⬆ Back to top

head

Returns the head of a list.

use lst[0] to return the first element of the passed list.

def head(lst):
  return lst[0]

Examples

head([1, 2, 3]); # 1

⬆ Back to top

initial

Returns all the elements of a list except the last one.

Use lst[0:-1] to return all but the last element of the list.

def initial(lst):
  return lst[0:-1]

Examples

initial([1, 2, 3]); # [1,2]

⬆ Back to top

initialize_2d_list

Initializes a 2D list of given width and height and value.

Use list comprehension and range() to generate h rows where each is a list with length h, initialized with val. If val is not provided, default to None.

Explain briefly how the snippet works.

def initialize_2d_list(w,h, val = None):
  return [[val for x in range(w)] for y in range(h)]

Examples

initialize_2d_list(2, 2, 0) # [[0,0], [0,0]]

⬆ Back to top

initialize_list_with_range

Initializes a list containing the numbers in the specified range where start and end are inclusive with their common difference step.

Use list and range() to generate a list of the appropriate length, filled with the desired values in the given range. Omit start to use the default value of 0. Omit step to use the default value of 1.

def initialize_list_with_range(end, start = 0, step = 1):
  return list(range(start, end + 1, step))

Examples

initialize_list_with_range(5) # [0, 1, 2, 3, 4, 5]
initialize_list_with_range(7,3) # [3, 4, 5, 6, 7]
initialize_list_with_range(9,0,2) # [0, 2, 4, 6, 8]

⬆ Back to top

initialize_list_with_values

Initializes and fills a list with the specified value.

Use list comprehension and range() to generate a list of length equal to n, filled with the desired values. Omit val to use the default value of 0.

def initialize_list_with_values(n, val = 0):
  return [val for x in range(n)]

Examples

initialize_list_with_values(5, 2) # [2, 2, 2, 2, 2]

⬆ Back to top

intersection

Returns a list of elements that exist in both lists.

Create a set from b, then use list comprehension on a to only keep values contained in both lists.

def intersection(a, b):
  _b = set(b)
  return [item for item in a if item in _b]

Examples

intersection([1, 2, 3], [4, 3, 2]) # [2, 3]

⬆ Back to top

intersection_by

Returns a list of elements that exist in both lists, after applying the provided function to each list element of both.

Create a set by applying fn to each element in b, then use list comprehension in combination with fn on a to only keep values contained in both lists.

def intersection_by(a, b, fn):
  _b = set(map(fn, b))
  return [item for item in a if fn(item) in _b]

Examples

from math import floor
intersection_by([2.1, 1.2], [2.3, 3.4],floor) # [2.1]

⬆ Back to top

last

Returns the last element in a list.

use lst[-1] to return the last element of the passed list.

def last(lst):
  return lst[-1]

Examples

last([1, 2, 3]) # 3

⬆ Back to top

longest_item

Takes any number of iterable objects or objects with a length property and returns the longest one. If multiple objects have the same length, the first one will be returned.

Use max() with len as the key to return the item with the greatest length.

def longest_item(*args):
  return max(args, key = len)

Examples

longest_item('this', 'is', 'a', 'testcase') # 'testcase'
longest_item([1, 2, 3], [1, 2], [1, 2, 3, 4, 5]) # [1, 2, 3, 4, 5]
longest_item([1, 2, 3], 'foobar') # 'foobar'

⬆ Back to top

max_n

Returns the n maximum elements from the provided list. If n is greater than or equal to the provided list's length, then return the original list (sorted in descending order).

Use sorted() to sort the list, [:n] to get the specified number of elements. Omit the second argument, n, to get a one-element list.

def max_n(lst, n=1):
  return sorted(lst, reverse=True)[:n]

Examples

max_n([1, 2, 3]) # [3]
max_n([1, 2, 3], 2) # [3,2]

⬆ Back to top

min_n

Returns the n minimum elements from the provided list. If n is greater than or equal to the provided list's length, then return the original list (sorted in ascending order).

Use sorted() to sort the list, [:n]to get the specified number of elements. Omit the second argument,n`, to get a one-element list.

def min_n(lst, n=1):
  return sorted(lst, reverse=False)[:n]

Examples

min_n([1, 2, 3]) # [1]
min_n([1, 2, 3], 2) # [1,2]

⬆ Back to top

none

Returns False if the provided function returns True for at least one element in the list, True otherwise.

Iterate over the elements of the list to test if every element in the list returns False based on fn. Omit the seconds argument, fn, to check if all elements are False.

def none(lst, fn=lambda x: not not x):
  for el in lst:
    if fn(el):
      return False
  return True

Examples

none([0, 1, 2, 0], lambda x: x >= 2 ) # False
none([0, 0, 0]) # True

⬆ Back to top

offset

Moves the specified amount of elements to the end of the list.

Use lst[offset:] and lst[:offset] to get the two slices of the list and combine them before returning.

Explain briefly how the snippet works.

def offset(lst, offset):
  return lst[offset:] + lst[:offset]

Examples

offset([1, 2, 3, 4, 5], 2) # [3, 4, 5, 1, 2]
offset([1, 2, 3, 4, 5], -2) # [4, 5, 1, 2, 3]

⬆ Back to top

sample

Returns a random element from an array.

Use randint() to generate a random number that corresponds to an index in the list, return the element at that index.

from random import randint

def sample(lst):
  return lst[randint(0, len(lst) - 1)]

Examples

sample([3, 7, 9, 11]) # 9

⬆ Back to top

shuffle

Randomizes the order of the values of an list, returning a new list.

Uses the Fisher-Yates algorithm to reorder the elements of the list.

from copy import deepcopy
from random import randint

def shuffle(lst):
  temp_lst = deepcopy(lst)
  m = len(temp_lst)
  while (m):
    m -= 1
    i = randint(0, m)
    temp_lst[m], temp_lst[i] = temp_lst[i], temp_lst[m]
  return temp_lst

Examples

foo = [1,2,3]
shuffle(foo) # [2,3,1] , foo = [1,2,3]

⬆ Back to top

similarity

Returns a list of elements that exist in both lists.

Use list comprehension on a to only keep values contained in both lists.

def similarity(a, b):
  return [item for item in a if item in b]

Examples

similarity([1, 2, 3], [1, 2, 4]) # [1, 2]

⬆ Back to top

some

Returns True if the provided function returns True for at least one element in the list, False otherwise.

Iterate over the elements of the list to test if every element in the list returns True based on fn. Omit the seconds argument, fn, to check if all elements are True.

def some(lst, fn=lambda x: not not x):
  for el in lst:
    if fn(el):
      return True
  return False

Examples

some([0, 1, 2, 0], lambda x: x >= 2 ) # True
some([0, 0, 1, 0]) # True

⬆ Back to top

spread

Flattens a list, by spreading its elements into a new list.

Loop over elements, use list.extend() if the element is a list, list.append() otherwise.

def spread(arg):
  ret = []
  for i in arg:
    if isinstance(i, list):
      ret.extend(i)
    else:
      ret.append(i)
  return ret

Examples

spread([1,2,3,[4,5,6],[7],8,9]) # [1,2,3,4,5,6,7,8,9]

⬆ Back to top

symmetric_difference

Returns the symmetric difference between two iterables, without filtering out duplicate values.

Create a set from each list, then use list comprehension on each one to only keep values not contained in the previously created set of the other.

def symmetric_difference(a, b):
  _a, _b = set(a), set(b)
  return [item for item in a if item not in _b] + [item for item in b if item not in _a]

Examples

symmetric_difference([1, 2, 3], [1, 2, 4]) # [3, 4]

⬆ Back to top

symmetric_difference_by

Returns the symmetric difference between two lists, after applying the provided function to each list element of both.

Create a set by applying fn to each element in every list, then use list comprehension in combination with fn on each one to only keep values not contained in the previously created set of the other.

def symmetric_difference_by(a, b, fn):
  _a, _b = set(map(fn, a)), set(map(fn, b))
  return [item for item in a if fn(item) not in _b] + [item for item in b if fn(item) not in _a]

Examples

from math import floor
symmetric_difference_by([2.1, 1.2], [2.3, 3.4],floor) # [1.2, 3.4]

⬆ Back to top

tail

Returns all elements in a list except for the first one.

Return lst[1:] if the list's length is more than 1, otherwise, return the whole list.

def tail(lst):
  return lst[1:] if len(lst) > 1 else lst

Examples

tail([1, 2, 3]); # [2,3]
tail([1]); # [1]

⬆ Back to top

union

Returns every element that exists in any of the two lists once.

Create a set with all values of a and b and convert to a list.

def union(a,b):
  return list(set(a + b))

Examples

union([1, 2, 3], [4, 3, 2]) # [1,2,3,4]

⬆ Back to top

union_by

Returns every element that exists in any of the two lists once, after applying the provided function to each element of both.

Create a set by applying fn to each element in a, then use list comprehension in combination with fn on b to only keep values not contained in the previously created set, _a. Finally, create a set from the previous result and a and transform it into a list

def union_by(a,b,fn):
  _a = set(map(fn, a))
  return list(set(a + [item for item in b if fn(item) not in _a]))

Examples

from math import floor
union_by([2.1], [1.2, 2.3], floor) # [2.1, 1.2]

⬆ Back to top

unique_elements

Returns the unique elements in a given list.

Create a set from the list to discard duplicated values, then return a list from it.

def unique_elements(li):
  return list(set(li))

Examples

unique_elements([1, 2, 2, 3, 4, 3]) # [1, 2, 3, 4]

⬆ Back to top

zip

Creates a list of elements, grouped based on the position in the original lists.

Use max combined with list comprehension to get the length of the longest list in the arguments. Loop for max_length times grouping elements. If lengths of lists vary, use fill_value (defaults to None).

def zip(*args, fillvalue=None):
  max_length = max([len(lst) for lst in args])
  result = []
  for i in range(max_length):
    result.append([
      args[k][i] if i < len(args[k]) else fillvalue for k in range(len(args))
    ])
  return result

Examples

zip(['a', 'b'], [1, 2], [True, False]) # [['a', 1, True], ['b', 2, False]]
zip(['a'], [1, 2], [True, False]) # [['a', 1, True], [None, 2, False]]
zip(['a'], [1, 2], [True, False], fill_value = '_') # [['a', 1, True], ['_', 2, False]]

⬆ Back to top

---

Math

average

Returns the average of two or more numbers.

Use sum() to sum all of the args provided, divide by len(args).

def average(*args):
  return sum(args, 0.0) / len(args)

Examples

average(*[1, 2, 3]) # 2.0
average(1, 2, 3) # 2.0

⬆ Back to top

average_by

Returns the average of a list, after mapping each element to a value using the provided function.

Use map() to map each element to the value returned by fn. Use sum() to sum all of the mapped values, divide by len(lst).

def average_by(lst, fn=lambda x: x):
  return sum(map(fn, lst), 0.0) / len(lst)

Examples

average_by([{ 'n': 4 }, { 'n': 2 }, { 'n': 8 }, { 'n': 6 }], lambda x: x['n']) # 5.0

⬆ Back to top

clamp_number

Clamps num within the inclusive range specified by the boundary values a and b.

If num falls within the range, return num. Otherwise, return the nearest number in the range.

def clamp_number(num,a,b):
  return max(min(num, max(a,b)),min(a,b))

Examples

clamp_number(2, 3, 5) # 3
clamp_number(1, -1, -5) # -1

⬆ Back to top

digitize

Converts a number to an array of digits.

Use map() combined with int on the string representation of n and return a list from the result.

def digitize(n):
  return list(map(int, str(n)))

Examples

digitize(123) # [1, 2, 3]

⬆ Back to top

factorial

Calculates the factorial of a number.

Use recursion. If num is less than or equal to 1, return 1. Otherwise, return the product of num and the factorial of num - 1. Throws an exception if num is a negative or a floating point number.

def factorial(num):
  if not ((num >= 0) & (num % 1 == 0)):
    raise Exception(
      f"Number( {num} ) can't be floating point or negative ")
  return 1 if num == 0 else num * factorial(num - 1)

Examples

factorial(6) # 720

⬆ Back to top

fibonacci

Generates an array, containing the Fibonacci sequence, up until the nth term.

Starting with 0 and 1, use list.apoend() to add the sum of the last two numbers of the list to the end of the list, until the length of the list reaches n. If nis less or equal to0, return a list containing 0`.

def fibonacci(n):
  if n <= 0:
    return [0]

  sequence = [0, 1]
  while len(sequence) <= n:
    next_value = sequence[len(sequence) - 1] + sequence[len(sequence) - 2]
    sequence.append(next_value)

  return sequence

Examples

fibonacci(7) # [0, 1, 1, 2, 3, 5, 8, 13]

⬆ Back to top

gcd

Calculates the greatest common divisor of a list of numbers.

Use reduce() and math.gcd over the given list.

from functools import reduce
import math

def gcd(numbers):
  return reduce(math.gcd, numbers)

Examples

gcd([8,36,28]) # 4

⬆ Back to top

in_range

Checks if the given number falls within the given range.

Use arithmetic comparison to check if the given number is in the specified range. If the second parameter, end, is not specified, the range is considered to be from 0 to start.

def in_range(n, start, end = 0):
  if (start > end):
    end, start = start, end
  return start <= n <= end

Examples

in_range(3, 2, 5); # True
in_range(3, 4); # True
in_range(2, 3, 5); # False
in_range(3, 2); # False

⬆ Back to top

is_divisible

Checks if the first numeric argument is divisible by the second one.

Use the modulo operator (%) to check if the remainder is equal to 0.

def is_divisible(dividend, divisor):
  return dividend % divisor == 0

Examples

is_divisible(6, 3) # True

⬆ Back to top

is_even

Returns True if the given number is even, False otherwise.

Checks whether a number is odd or even using the modulo (%) operator. Returns True if the number is even, False if the number is odd.

def is_even(num):
  return num % 2 == 0

Examples

is_even(3) # False

⬆ Back to top

is_odd

Returns True if the given number is odd, False otherwise.

Checks whether a number is even or odd using the modulo (%) operator. Returns True if the number is odd, False if the number is even.

def is_odd(num):
  return num % 2 != 0

Examples

is_odd(3) # True

⬆ Back to top

lcm

Returns the least common multiple of two or more numbers.

Define a function, spread, that uses either list.extend() or list.append() on each element in a list to flatten it. Use math.gcd() and lcm(x,y) = x * y / gcd(x,y) to determine the least common multiple.

from functools import reduce
import math

def spread(arg):
  ret = []
  for i in arg:
    if isinstance(i, list):
      ret.extend(i)
    else:
      ret.append(i)
  return ret

def lcm(*args):
  numbers = []
  numbers.extend(spread(list(args)))

  def _lcm(x, y):
    return int(x * y / math.gcd(x, y))

  return reduce((lambda x, y: _lcm(x, y)), numbers)

Examples

lcm(12, 7) # 84
lcm([1, 3, 4], 5) # 60

⬆ Back to top

max_by

Returns the maximum value of a list, after mapping each element to a value using the provided function.

Use map() with fn to map each element to a value using the provided function, convert to a list and use max() to return the maximum value.

def max_by(lst, fn):
  return max(list(map(fn,lst)))

Examples

max_by([{ 'n': 4 }, { 'n': 2 }, { 'n': 8 }, { 'n': 6 }], lambda v : v['n']) # 8

⬆ Back to top

min_by

Returns the minimum value of a list, after mapping each element to a value using the provided function.

Use map() with fn to map each element to a value using the provided function, convert to a list and use min() to return the minimum value.

def min_by(lst, fn):
  return min(list(map(fn,lst)))

Examples

min_by([{ 'n': 4 }, { 'n': 2 }, { 'n': 8 }, { 'n': 6 }], lambda v : v['n']) # 2

⬆ Back to top

rads_to_degrees

Converts an angle from radians to degrees.

Use math.pi and the radian to degree formula to convert the angle from radians to degrees.

import math

def rads_to_degrees(rad):
  return (rad * 180.0) / math.pi

Examples

import math
rads_to_degrees(math.pi / 2) # 90.0

⬆ Back to top

sum_by

Returns the sum of a list, after mapping each element to a value using the provided function.

Use map() with fn to map each element to a value using the provided function, convert to a list and use sum() to return the sum of the values.

def sum_by(lst, fn):
  return sum(list(map(fn,lst)))

Examples

sum_by([{ 'n': 4 }, { 'n': 2 }, { 'n': 8 }, { 'n': 6 }], lambda v : v['n']) # 20

⬆ Back to top

---

Object

keys_only

Returns a flat list of all the keys in a flat dictionary.

Use dict.keys() to return the keys in the given dictionary. Return a list() of the previous result.

def keys_only(flat_dict):
  return list(flat_dict.keys())

Examples

ages = {
  "Peter": 10,
  "Isabel": 11,
  "Anna": 9,
}
keys_only(ages) # ['Peter', 'Isabel', 'Anna']

⬆ Back to top

map_values

Creates an object with the same keys as the provided object and values generated by running the provided function for each value.

Use dict.keys() to iterate over the object's keys, assigning the values produced by fn to each key of a new object.

def map_values(obj, fn):
  ret = {}
  for key in obj.keys():
    ret[key] = fn(obj[key])
  return ret

Examples

users = {
  'fred': { 'user': 'fred', 'age': 40 },
  'pebbles': { 'user': 'pebbles', 'age': 1 }
}

map_values(users, lambda u : u['age']) # {'fred': 40, 'pebbles': 1}

⬆ Back to top

values_only

Returns a flat list of all the values in a flat dictionary.

Use dict.values() to return the values in the given dictionary. Return a list() of the previous result.

def values_only(dict):
  return list(flat_dict.values())

Examples

ages = {
  "Peter": 10,
  "Isabel": 11,
  "Anna": 9,
}
values_only(ages) # [10, 11, 9]

⬆ Back to top

---

String

byte_size

Returns the length of a string in bytes.

Use string.encode('utf-8') to encode the given string and return its length.

def byte_size(string):
  return len(string.encode('utf-8'))

Examples

byte_size('😀') # 4
byte_size('Hello World') # 11

⬆ Back to top

camel

Converts a string to camelcase.

Break the string into words and combine them capitalizing the first letter of each word, using a regexp, title() and lower.

import re

def camel(s):
  s = re.sub(r"(\s|_|-)+", " ", s).title().replace(" ", "")
  return s[0].lower() + s[1:]

Examples

camel('some_database_field_name'); # 'someDatabaseFieldName'
camel('Some label that needs to be camelized'); # 'someLabelThatNeedsToBeCamelized'
camel('some-javascript-property'); # 'someJavascriptProperty'
camel('some-mixed_string with spaces_underscores-and-hyphens'); # 'someMixedStringWithSpacesUnderscoresAndHyphens'

⬆ Back to top

capitalize

Capitalizes the first letter of a string.

Capitalize the first letter of the string and then add it with rest of the string. Omit the lower_rest parameter to keep the rest of the string intact, or set it to True to convert to lowercase.

def capitalize(string, lower_rest=False):
  return string[:1].upper() + (string[1:].lower() if lower_rest else string[1:])

Examples

capitalize('fooBar') # 'FooBar'
capitalize('fooBar', True) # 'Foobar'

⬆ Back to top

capitalize_every_word

Capitalizes the first letter of every word in a string.

Use string.title() to capitalize first letter of every word in the string.

def capitalize_every_word(string):
  return string.title()

Examples

capitalize_every_word('hello world!') # 'Hello World!'

⬆ Back to top

decapitalize

Decapitalizes the first letter of a string.

Decapitalize the first letter of the string and then add it with rest of the string. Omit the upper_rest parameter to keep the rest of the string intact, or set it to True to convert to uppercase.

def decapitalize(string, upper_rest=False):
  return str[:1].lower() + (str[1:].upper() if upper_rest else str[1:])

Examples

decapitalize('FooBar') # 'fooBar'
decapitalize('FooBar', True) # 'fOOBAR'

⬆ Back to top

is_anagram

Checks if a string is an anagram of another string (case-insensitive, ignores spaces, punctuation and special characters).

Use str.replace() to remove spaces from both strings. Compare the lengths of the two strings, return False if they are not equal. Use sorted() on both strings and compare the results.

def is_anagram(str1, str2):
  _str1, _str2 = str1.replace(" ", ""), str2.replace(" ", "")

  if len(_str1) != len(_str2):
    return False
  else:
    return sorted(_str1.lower()) == sorted(_str2.lower())

Examples

is_anagram("anagram", "Nag a ram")  # True

⬆ Back to top

is_lower_case

Checks if a string is lower case.

Convert the given string to lower case, using str.lower() and compare it to the original.

def is_lower_case(string):
  return string == string.lower()

Examples

is_lower_case('abc') # True
is_lower_case('a3@$') # True
is_lower_case('Ab4') # False

⬆ Back to top

is_upper_case

Checks if a string is upper case.

Convert the given string to upper case, using str.upper() and compare it to the original.

def is_upper_case(string):
  return string == string.upper()

Examples

is_upper_case('ABC') # True
is_upper_case('a3@$') # False
is_upper_case('aB4') # False

⬆ Back to top

kebab

Converts a string to kebab case.

Break the string into words and combine them adding - as a separator, using a regexp.

import re

def kebab(str):
  return re.sub(r"(\s|_|-)+","-",
    re.sub(r"[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+",
    lambda mo: mo.group(0).lower(),str)
  )

Examples

kebab('camelCase'); # 'camel-case'
kebab('some text'); # 'some-text'
kebab('some-mixed_string With spaces_underscores-and-hyphens'); # 'some-mixed-string-with-spaces-underscores-and-hyphens'
kebab('AllThe-small Things'); # "all-the-small-things"

⬆ Back to top

palindrome

Returns True if the given string is a palindrome, False otherwise.

Use str.lower() and re.sub() to convert to lowercase and remove non-alphanumeric characters from the given string. Then, compare the new string with its reverse.

from re import sub

def palindrome(string):
  s = sub('[\W_]', '', string.lower())
  return s == s[::-1]

Examples

palindrome('taco cat') # True

⬆ Back to top

snake

Converts a string to snake case.

Break the string into words and combine them adding _-_ as a separator, using a regexp.

import re

def snake(str):
  return re.sub(r"(\s|_|-)+","-",
    re.sub(r"[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+",
    lambda mo: mo.group(0).lower(),str)
  )

Examples

snake('camelCase'); # 'camel_case'
snake('some text'); # 'some_text'
snake('some-mixed_string With spaces_underscores-and-hyphens'); # 'some_mixed_string_with_spaces_underscores_and_hyphens'
snake('AllThe-small Things'); # "all_the_smal_things"

⬆ Back to top

split_lines

Splits a multiline string into a list of lines.

Use str.split() and '\n' to match line breaks and create a list.

def split_lines(str):
  return str.split('\n')

Examples

split_lines('This\nis a\nmultiline\nstring.\n') # 'This\nis a\nmultiline\nstring.\n'

⬆ Back to top

---

Utility

cast_list

Casts the provided value as an array if it's not one.

Use isinstance() to check if the given value is a list and return it as-is or encapsulated in a list accordingly.

def cast_list(val):
  return val if isinstance(val, list) else [val]

Examples

cast_list('foo'); # ['foo']
cast_list([1]); # [1]

⬆ Back to top

Collaborators

Angelos Chalaris	Stefan Feješ	Rohit Tanwar

Credits

This README is built using markdown-builder.