30-seconds-of-python-code 
Welcome to 30-seconds-of-python-code!
If you've come here from javascript land then you should be aware that this project uses python 3, therefore not all snippets will work as expected in every python interpreter or on system. You'll need to check your python version with the command python -v. If you need help installing the latest stable release of python 3 on your system checkout docs.python.org if you run into trouble make sure you research stackoverflow. Eventually it might be worth looking into how to set up a virtual environment for python projects with virtualenv or even a tool like anaconda.
This project contains plenty of useful snippets which can help beginners and newcomers quickly ramp-up on grasping python 3's syntax.
Table of contents
List
View contents
all_equalall_uniquebifurcatebifurcate_bychunkcompactcount_bycount_occurencesdeep_flattendifferencedifference_byeveryevery_nthfilter_non_uniquegroup_byhas_duplicatesheadinitialinitialize_2d_listinitialize_list_with_rangeinitialize_list_with_valuesintersectionintersection_bylastlongest_itemmax_nmin_nnoneoffsetsampleshufflesimilaritysomespreadtailunique_elementszip
Math
View contents
Object
View contents
String
View contents
Utility
View contents
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.
```py
def all_equal(lst):
return lst[1:] == lst[:-1]
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def all_unique(lst):
return len(lst) == len(set(lst))
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
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]
]
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def bifurcate_by(lst, fn):
return [
[x for x in lst if fn(x)],
[x for x in lst if not fn(x)]
]
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
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)))))
<details>
<summary>Examples</summary>
```python
undefined
compact
Removes falsey values from a list.
Use filter() to filter out falsey values (False, None, 0, and "").
```py
def compact(lst):
return list(filter(bool, lst))
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
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
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def count_occurrences(lst, val):
return len([x for x in lst if x == val and type(x) == type(val)])
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
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
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def difference(a, b):
_b = set(b)
return [item for item in a if item not in _b]
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def difference_by(a, b, fn):
_b = set(map(fn, b))
return [item for item in a if fn(item) not in _b]
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def every(lst, fn=lambda x: not not x):
for el in lst:
if not fn(el):
return False
return True
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def every_nth(lst, nth):
return lst[1::nth]
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def filter_non_unique(lst):
return [item for item in lst if lst.count(item) == 1]
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
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
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def has_duplicates(lst):
return len(lst) != len(set(lst))
<details>
<summary>Examples</summary>
```python
undefined
head
Returns the head of a list.
use lst[0] to return the first element of the passed list.
```py
def head(lst):
return lst[0]
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def initial(lst):
return lst[0:-1]
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def initialize_2d_list(w,h, val = None):
return [[val for x in range(w)] for y in range(h)]
<details>
<summary>Examples</summary>
```python
undefined
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 comprehension 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.
```py
def initialize_list_with_range(end, start = 0, step = 1):
return [x for x in range(start, end + 1, step)]
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def initialize_list_with_values(n, val = 0):
return [val for x in range(n)]
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def intersection(a, b):
_b = set(b)
return [item for item in a if item in _b]
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def intersection_by(a, b, fn):
_b = set(map(fn, b))
return [item for item in a if fn(item) in _b]
<details>
<summary>Examples</summary>
```python
undefined
last
Returns the last element in a list.
use lst[-1] to return the last element of the passed list.
```py
def last(lst):
return lst[-1]
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def longest_item(*args):
return max(args, key = len)
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def max_n(lst, n=1):
return sorted(lst, reverse=True)[:n]
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def min_n(lst, n=1):
return sorted(lst, reverse=False)[:n]
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def none(lst, fn=lambda x: not not x):
for el in lst:
if fn(el):
return False
return True
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def offset(lst, offset):
return lst[offset:] + lst[:offset]
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
from random import randint
def sample(lst):
return lst[randint(0, len(lst) - 1)]
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
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
<details>
<summary>Examples</summary>
```python
undefined
similarity
Returns a list of elements that exist in both lists.
Use list comprehension on a to only keep values contained in both lists.
```py
def similarity(a, b):
return [item for item in a if item in b]
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def some(lst, fn=lambda x: not not x):
for el in lst:
if fn(el):
return True
return False
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def spread(arg):
ret = []
for i in arg:
if isinstance(i, list):
ret.extend(i)
else:
ret.append(i)
return ret
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def tail(lst):
return lst[1:] if len(lst) > 1 else lst
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def unique_elements(li):
return list(set(li))
<details>
<summary>Examples</summary>
```python
undefined
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).
```py
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
<details>
<summary>Examples</summary>
```python
undefined
Math
average
Returns the average of two or more numbers.
Use sum() to sum all of the args provided, divide by len(args).
```py
def average(*args):
return sum(args, 0.0) / len(args)
<details>
<summary>Examples</summary>
```python
undefined
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).
```py
def average_by(lst, fn=lambda x: x):
return sum(map(fn, lst), 0.0) / len(lst)
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def clamp_number(num,a,b):
return max(min(num, max(a,b)),min(a,b))
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def digitize(n):
return list(map(int, str(n)))
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
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)
<details>
<summary>Examples</summary>
```python
undefined
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`.
```py
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
<details>
<summary>Examples</summary>
```python
undefined
gcd
Calculates the greatest common divisor of a list of numbers.
Use reduce() and math.gcd over the given list.
```py
from functools import reduce
import math
def gcd(numbers):
return reduce(math.gcd, numbers)
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def in_range(n, start, end = 0):
if (start > end):
end, start = start, end
return start <= n <= end
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def is_divisible(dividend, divisor):
return dividend % divisor == 0
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def is_even(num):
return num % 2 == 0
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def is_odd(num):
return num % 2 == `0`
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
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)
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def max_by(lst, fn):
return max(list(map(fn,lst)))
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def min_by(lst, fn):
return min(list(map(fn,lst)))
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
import math
def rads_to_degrees(rad):
return (rad * 180.0) / math.pi
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def keys_only(flat_dict):
return list(flat_dict.keys())
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def map_values(obj, fn):
ret = {}
for key in obj.keys():
ret[key] = fn(obj[key])
return ret
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def values_only(dict):
return list(flat_dict.values())
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def byte_size(string):
return len(string.encode('utf-8'))
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def capitalize(string, lower_rest=False):
return string[:1].upper() + (string[1:].lower() if lower_rest else string[1:])
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def capitalize_every_word(string):
return string.title()
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def decapitalize(string, upper_rest=False):
return str[:1].lower() + (str[1:].upper() if upper_rest else str[1:])
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
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())
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def is_lower_case(string):
return string == string.lower()
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def is_upper_case(string):
return string == string.upper()
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
from re import sub
def palindrome(string):
s = sub('[\W_]', '', string.lower())
return s == s[::-1]
<details>
<summary>Examples</summary>
```python
undefined
split_lines
Splits a multiline string into a list of lines.
Use str.split() and '\n' to match line breaks and create a list.
```py
def split_lines(str):
str.split('\n')
<details>
<summary>Examples</summary>
```python
undefined
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.
```py
def cast_list(val):
return val if isinstance(val, list) else [val]
<details>
<summary>Examples</summary>
```python
undefined
Credits
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License
