Basic Python 3 grammar (some Python iterations)

Overview

You will study the basic grammar of Python 3 by referring to "Introduction to Python 3" by O'Reilly Japan. I hope it will be helpful for those who want to study Python in the same way.

Iterative processing

Let's compare the code that retrieves the values in the list by iterating.

Iterative processing written normally

>>> target = ['AAA', 'BBB', 'CCC']
>>> current = 0
>>> while current < len(target):
...     print(target[current])
...     current += 1
...
AAA
BBB
CCC

Iterative processing written like Python

>>> target = ['AAA', 'BBB', 'CCC']
>>> for out in target:
...     print(out)
...
AAA
BBB
CCC

The second code is better Python-like code. Since a list is a Python iterator (corresponding to an iterator) object, processing it with a for statement retrieves the elements of the list one by one.

for statement

Besides lists, there are Python iterator objects like strings, tuples, dictionaries, sets, and more.

String

>>> target = 'python'
>>> for out in target:
...     print(out)
...
p
y
t
h
o
n

dictionary

Key removal (1)

>>> num = {0:'zero', 1:'one', 2:'two'}
>>> for out in num:
...     print(out)
...
0
1
2

Key removal (2)

>>> num = {0:'zero', 1:'one', 2:'two'}
>>> for out in num.keys():
...     print(out)
...
0
1
2

Extracting the value

>>> num = {0:'zero', 1:'one', 2:'two'}
>>> for out in num.values():
...     print(out)
...
zero
one
two

Extraction in tuple format

>>> num = {0:'zero', 1:'one', 2:'two'}
>>> for out in num.items():
...     print(out)
...
(0, 'zero')
(1, 'one')
(2, 'two')

Extraction in tuple format (application)

When processing retrieval and assignment in one step

>>> num = {0:'zero', 1:'one', 2:'two'}
>>> for key, value in num.items():
...     print('key:', key, 'value:', value)
...
key: 0 value: zero
key: 1 value: one
key: 2 value: two

Iterative processing using zip ()

You can use zip () to iterate over multiple sequences in parallel.

>>> list1 = ['1', '2', '3']
>>> list2 = ['A', 'B', 'C']
>>> list3 = ['one', 'two', 'three']
>>> for out1, out2, out3 in zip(list1, list2, list3):
...     print('list1:', out1, 'list2', out2, 'list3', out3)
...
list1: 1 list2 A list3 one
list1: 2 list2 B list3 two
list1: 3 list2 C list3 three

Generate a list with the return value of zip ()

>>> list1 = ['1', '2', '3']
>>> list2 = ['A', 'B', 'C']
>>> list( zip(list1, list2) )
[('1', 'A'), ('2', 'B'), ('3', 'C')]

Generate a dictionary with the return value of zip ()

>>> list1 = ['1', '2', '3']
>>> list2 = ['A', 'B', 'C']
>>> dict( zip(list1, list2) )
{'1': 'A', '2': 'B', '3': 'C'}

Creating a numeric sequence with range ()

Operation image

>>> for x in range(0, 3):
...     print(x)
...
0
1
2

Creating a list of numeric sequences

>>> list( range(0, 3) )
[0, 1, 2]