Useful tricks related to list and for statements in Python

** Do the same for each element of list --map **

map.py

def add1(str):         #A function that adds a 1 character to the end of a character
      return str+'1'
    
list_str = ['a', 'b', 'c']
map(add1, list_str)

Out[3]: ['a1', 'b1', 'c1']

You can do the same by writing as follows.

map.py

map(lambda x : x+'1', list_str)

This is still the same (list comprehension notation)

map.py

[x+'1' for x in list_str]

** Extract only conditional elements --filter **

Extract only the elements with 3 characters from the list.

filter.py

list_words = ['toy', 'cat', 'dog', 'girl', 'house', 'boy']
filter(lambda x : len(x)==3, list_words)

Out[7]: ['toy', 'cat', 'dog', 'boy']

This is still the same (list comprehension notation)

map.py

[x for x in list_words if len(x)==3]

** Duplicate list and how to handle it --set **

set.py

list_words2 = ['toy', 'cat', 'dog', 'girl', 'house', 'boy', 'toy', 'toy', 'cat', 'dog']
list_words2_unique = set(list_words2)

Create a set object that eliminates duplicate elements in the list

list_words2_unique
Out[8]: set(['boy', 'toy', 'house', 'dog', 'cat', 'girl'])

You can add elements to the set object with the method "add", Adding duplicate elements does not change Changes only occur for new elements to the list

set.py

list_words2_unique.add('dog')
list_words2_unique

Out[16]:
{'boy', 'cat', 'dog', 'girl', 'house', 'toy'}

set.py

list_words2_unique.add('sheep')  #Add an element that is not in the list
list_words2_unique

Out[17]:
{'boy', 'cat', 'dog', 'girl', 'house', 'sheep', 'toy'} #Will be added

You can also use Union to union with another list.

set.py

list_words2_unique.union(['lion', 'cow', 'dog', 'cat'])

Out[18]:
{'boy', 'cat', 'cow', 'dog', 'girl', 'house', 'lion', 'sheep', 'toy'}

** I want to use serial numbers in For statements-enumerate **

How to automatically assign serial numbers with a for statement

enumerate.py

list_words = ['toy', 'cat', 'dog', 'girl', 'house', 'boy']

for i, word in enumerate(list_words):　#i is a serial number and word is a list element
    print (i, word)

Out[19]: 
       (0, 'toy')
       (1, 'cat')
       (2, 'dog')
       (3, 'girl')
       (4, 'house')
       (5, 'boy')

** Two-element For statement --zip **

zip.py

list_words = ['toy', 'cat', 'dog', 'girl', 'house', 'boy']
list_number =[21, 3, 12, 5, 6, 19]

#list to num_The element of number is list in word_Contains words elements
for num, word in zip(list_number, list_words):  
    print (num, word)

Out[20]: 
    (21, 'toy')
    (3, 'cat')
    (12, 'dog')
    (5, 'girl')
    (6, 'house')
    (19, 'boy')

If you write the above enumerate in zip (forcibly), it will be as follows.

length = len(list_words)

for i, word in zip(range(length), list_words):
        print (i, word)