What are some very practical Python skills?

1. Uniqueness

The following method can check whether there are duplicates in a given list, and use the set() attribute to delete them from the list.

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

2. Anagrams (words with the same letters in different orders)

This method can be used to check whether two strings are anagrams.

from collections import Counter
>>> Counter('abadfsdafsdfjsdaf')
Counter({'a': 4, 'd': 4, 'f': 4, 's': 3, 'b': 1, 'j': 1})

def anagram(first, second):
    return Counter(first) == Counter(second)
anagram("abcd3", "3acdb") # True

3. Memory

This code snippet can be used to check the memory usage of an object.

import sys 
variable = 30 
print(sys.getsizeof(variable)) # 28

4. Byte size

This method can output the byte size of the string.

print(len(''.encode('utf-8')))# 0
print(len('hellow sdfsdaf'.encode('utf-8'))) # 14

5. Print a string N times

This code segment can print a string multiple times without looping.

n = 2; 
s ="Programming"; 
print(s * n); # ProgrammingProgramming

6. Capitalize the first letter

The following code snippet only uses title() to capitalize the first letter of each word in the string.

s = "programming is awesome"
print(s.title()) # Programming Is Awesome

7. List subdivision

This method subdivides the list into lists of a specific size.

>>> list = list(range(12))
>>> size=3
>>> [list[i:i+size] for i in range(0,len(list), size)]
[[0, 1, 2], [3, 4, 5], [6, 7, 8], [9, 10, 11]]
>>>

8. Compression

The following code uses filter() to remove error values ​​(False, None, 0 and " ") from the list.

list(filter(bool, [0, 1, False, 2, '', 3, 'a', 's', 34]))

9. Counting

The following code can be used to swap the 2D array arrangement.

array = [['a', 'b'], ['c', 'd'], ['e', 'f']]
transposed = zip(*array)
print(transposed)  # [('a', 'c', 'e'), ('b', 'd', 'f')]

10. Chain comparison

The following code can perform multiple comparisons on various operators.

a = 3
print( 2 < a < 8) # True
print(1 == a < 2) # False

11. Comma separated

This code snippet converts a list of strings into a single string while separating each element in the list with a comma.

hobbies = ["basketball", "football", "swimming"]
print("My hobbies are: " + ", ".join(hobbies)) # My hobbies are: basketball, football, swimming

12. Vowel counting

This method can count the number of vowels ("a", "e", "i", "o", "u") in the string .

import re
print(len(re.findall(r'[aeiou]', 'foobar', re.IGNORECASE)))   # 3
print(len(re.findall(r'[aeiou]', 'gym', re.IGNORECASE)))   # 0

13. The first letter is lowercase

This method converts the first letter of the given string into lowercase mode.

'FooBar'[:1].lower() + 'FooBar'[1:] # 'fooBar'
'FooBar'[:1].lower() + 'FooBar'[1:]   # 'fooBar'

14. Expand the list

The following code uses a recursive method to expand a potentially deep 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
deep_flatten([1, [2], [[3], 4], 5])  # [1,2,3,4,5]
print(deep_flatten([1, [2], [[3], 4], 5]))  # [1,2,3,4,5]

15. Find the difference

This method keeps only the values ​​in the first iteration to find the difference between the two iterations

set([1,2,3])-set([1,2,4]) # [3]

16. Output the difference

The following method uses existing functions to find and output the difference between two lists.

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

17. Chain function call

The following method can call multiple functions in one line

def add(a, b):
    return a + b
def subtract(a, b):
    return a – b
a, b = 4, 5
print((subtract if a > b else add)(a, b)) # 9

18.

In Python3.5 and In the upgraded version, you can also execute the step code in the following way:

def merge_dictionaries(a, b):
    return {**a, **b}
a = { 'x': 1, 'y': 2}
b = { 'y': 3, 'z': 4}
print(merge_dictionaries(a, b)) # {'y': 3, 'x': 1, 'z': 4}

19. Convert two lists into fonts

The following method can convert two lists into fonts.

keys = ["a", "b", "c"] 
values = [2, 3, 4]
print(dict(zip(keys, values))) # {'a': 2, 'c': 4, 'b': 3}

20. The element with the highest frequency of occurrence

This method will output the element with the highest frequency of appearance in the list.

def most_frequent(list):
    return max(set(list), key = list.count)
list = [1,2,1,2,3,2,1,4,2]
most_frequent(list)

21. Palindrome (the same string is read forward and backward)

The following code checks whether the given string is a palindrome. First convert the string to lowercase, then remove non-alphabetic characters from it, and finally compare the new string version to the original version.

def palindrome(string):
    from re import sub
    s = sub('[\W_]', '', string.lower())
    return s == s[::-1]
palindrome('taco cat') # True

22. Calculator without if-else statements

The following code snippet shows how to write a simple calculator without if-else conditional statements.

import operator
action = {
 "+": operator.add,
 "-": operator.sub,
 "/": operator.truediv,
 "*": operator.mul,
 "**": pow
}
print(action['-'](50, 25)) # 25

23. Random sorting

This algorithm uses the Fisher-Yates algorithm to randomly sort the elements in the new 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

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

24. Expand the list

This method can only expand 2 levels of nested lists, not more than 2 levels

def spread(arg):
    ret = []
    for i in arg:
        if isinstance(i, list):
            ret.extend(i)
        else:
            ret.append(i)
    return ret
spread([1, 2, 3, [4, 5, 6], [7], 8, 9])  # [1,2,3,4,5,6,7,8,9]
print(spread([1, 2, 3, [4, 5,[10,11,12,132,4,[1,2,3,4,5,6]], 6], [7], 8, 9]))  #[1, 2, 3, 4, 5, [10, 11, 12, 132, 4, [1, 2, 3, 4, 5, 6]], 6, 7, 8, 9]

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