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Python 3 cheatsheet

I wanted to post my Python3 cheat sheet and some useful functions I use almost every day. These functions are no libraries needed making them easier to implement. As far as I learn more programming languages I'll create more cheat sheets, hope they'll be helpful.

My Python 3 Cheat sheet

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Usefull scripts:

Method: sort by key list

This function sort two list of the same lenght taking the first one as the key-list and making the second one dependent. This codes works only with two same size lists.

Method

def sorter(lst, elements):
    xy = zip(lst, elements)
    lst_sorted = [x for x, y in sorted(xy)]
    xy = zip(lst, elements)
    elements_sorted = [y for x, y in sorted(xy)]
    return lst_sorted, elements_sorted

Example

keys = [1, 3, 2, 6, 4, 8, 5, 10]
elements = ['dog', 'cat', 'monkey', 'lizard', 'eagle', 'spyder', 'snake', 'wolf']

# Calling the function
sorter(keys, elements)
output
([1, 2, 3, 4, 5, 6, 8, 10],
['dog', 'monkey', 'cat', 'eagle', 'snake', 'lizard', 'spyder', 'wolf'])

Method: entwine elements of two lists

This function takes two lists and interspersing all elements, starting by the first list element. For this function the same size lists are no needed.

Method:

def entwine(lst1, lst2):
    zipped = []
    a = max([len(lst1), len(lst2)])
    for i in range(a):
        try:
            zipped.append(lst1[i])
        except:
            pass
        try:
            zipped.append(lst2[i])
        except:
            pass
    return zipped

Example

lst_1 = ['alpha', 'bravo', 'charlie', 'delta', 'echo']
lst_2 = [1, 2, 5, 12, 18, 0]

entwine(lst_1, lst_2)
output
    ['alpha', 1, 'bravo', 2, 'charlie', 5, 'delta', 12, 'echo', 18, 0]

Method: counter items

This function counts each item of a list and outputs providing the frequency by item.

Method

def counter(lst):
    output = {}
    for value in lst:
        count = len([i for i in lst if i == value])
        output[value] = count
    return output

Example

lst = ['A', 'C', 'D', 'A', 'B', 'C', 'D', 'A']

grooping(lst)
Output
    {'A': 3, 'C': 2, 'D': 2, 'B': 1}

Method: permutate elements of a list

This function resolve all the possible permutations from a list with no elements repeated.

Method

def permute(lst):
    combi = []
    for i in range(len(lst)):
        for x in range(i, len(lst)):
            if lst[i] != lst[x]:
                combi.append([lst[i],lst[x]])
    return combi

Example

words = ['alpha', 'bravo', 'charlie']

permute(words)
Output
    [['alpha', 'bravo'], ['alpha', 'charlie'], ['bravo', 'charlie']]

Method: invert dictionary

This function invert a dictionary switching keys with values.

Method

def invert_dictionary(dictionary):
    all_dcts = []
    for k, v in dictionary.items():
        temp_dct = {}
        for token in v:
            temp_dct[token] = [k]
        all_dcts.append(temp_dct)
    inverted_dictionary = all_dcts[0]
    for dct in all_dcts[1:]:
        for k, v in dct.items():
            if k in inverted_dictionary.keys():
                inverted_dictionary[k] = inverted_dictionary[k] + v
            else:
                inverted_dictionary[k] = v
    return inverted_dictionary

Example

dictionary = {'a' : [1, 5, 9, 8], 'b' : [2, 3, 8, 0], 'c' : [8, 9, 0, 8]}

invert_dictionary(dictionary)
output
{1: ['a'],
 5: ['a'],
 9: ['a', 'c'],
 8: ['a', 'b', 'c'],
 2: ['b'],
 3: ['b'],
 0: ['b', 'c']}