Sorts one list based on another list containing the desired indexes.

Use zip() and sorted() to combine and sort the two lists, based on the values of indexes.

Use a list comprehension to get the first element of each pair from the result.

Use the reverse parameter in sorted() to sort the dictionary in reverse order, based on the third argument.

CODE:

def sort_by_indexes(lst, indexes, reverse=False):
return [val for (_, val) in sorted(zip(indexes, lst), key=lambda x: \
x[0], reverse=reverse)]

Example:

a = ['eggs', 'bread', 'oranges', 'jam', 'apples', 'milk']

b = [3, 2, 6, 4, 1, 5]

sort_by_indexes(a, b)

Output: ['apples', 'bread', 'eggs', 'jam', 'milk', 'oranges']

sort_by_indexes(a, b, True)

Output: ['oranges', 'milk', 'jam', 'eggs', 'bread', 'apples']

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unfold

Builds a list, using an iterator function and an initial seed value.

The iterator function accepts one argument (seed) and must always return a list with two elements ([value, nextSeed]) or False to terminate.
Use a generator function, fn_generator, that uses a while loop to call the iterator function and yield the value until it returns False.
Use a list comprehension to return the list that is produced by the generator, using the iterator function.

CODE:

def unfold(fn, seed):
  def fn_generator(val):
    while True: 
      val = fn(val[1])
      if val == False: break
      yield val[0]
  return [i for i in fn_generator([None, seed])]

f = lambda n: False if n > 50 else [-n, n + 10]
INPUT:
unfold(f, 10)

OUTPUT:
[-10, -20, -30, -40, -50]

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curry

Curries a function.

Use functools.partial() to return a new partial object which behaves like fn with the given arguments, args, partially applied.

CODE:

from functools import partial

def curry(fn, *args):
return partial(fn, *args)

Examples:

add = lambda x, y: x + y
add10 = curry(add, 10)
add10(20) # 30

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#Basics

Return Multiple Values From Functions.

Code:

def x():
    return 1, 2, 3, 4
a, b, c, d = x()

Input:
print(a, b, c, d)

Output:
1 2 3 4

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#Basics

Find The Most Frequent Value In A List

Code:

test = [1, 2, 3, 4, 2, 2, 3, 1, 4, 4, 4]
print(max(set(test), key = test.count))

Output:
4
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#Basics

Check The Memory Usage Of An Object.

Code:

import sys
x = 1
print(sys.getsizeof(x))

Output:
28

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#Basics

Checking if two words are anagrams

Code:

from collections import Counter
def is_anagram(str1, str2):
     return Counter(str1) == Counter(str2)
  
# or without having to import anything 
def is_anagram(str1, str2): 
    return sorted(str1) == sorted(str2) 

print(is_anagram('code', 'doce'))
print(is_anagram('python', 'yton'))

Output:
True
False

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#Basics

zip() function

When we need to join many iterator objects like lists to get a single list we can use the zip function. The result shows each item to be grouped with their respective items from the other lists.

Example:

Year = (1999, 2003, 2011, 2017)
Month = ("Mar", "Jun", "Jan", "Dec")
Day = (11,21,13,5)
print zip(Year,Month,Day)

Output:
[(1999, 'Mar', 11), (2003, 'Jun', 21), (2011, 'Jan', 13), (2017, 'Dec', 5)]

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#Basics

Transpose a Matrix

Transposing a matrix involves converting columns into rows. In python we can achieve it by designing some loop structure to iterate through the elements in the matrix and change their places or we can use the following script involving zip function in conjunction with the * operator to unzip a list which becomes a transpose of the given matrix.

Example:

x = [[31,17],
[40 ,51],
[13 ,12]]
print (zip(*x))

Output:
[(31, 40, 13), (17, 51, 12)]

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#Basics

The _ Operator

The _ operator might be something that you might not have heard of. Here _ is the output of the last executed expression. Let’s check how it works.


Example:

>>> 2+ 3
5
>>> _ # the _ operator, it will return the output of the last executed statement.
>>> 5

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#Basics

Swap keys and values of a dictionary

dictionary = {"a": 1, "b": 2, "c": 3}

reversed_dictionary = {j: i for i, j in dictionary.items()}

print(reversed)

Output:
{1: 'a', 2: 'b', 3: 'c'}

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#Basics

Condition inside the print function

def is_positive(number):
print("Positive" if number > 0 else "Negative")


is_positive(-3)

Output:

Negative

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#Basics

Convert a value into a complex number

print(complex(10, 2)) 

Output:
(10+2j)

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