How to write a good python loop

To write a good loop in Python, you don’t need a for statement! ! !

First, let’s take a step back and look at the intuition behind writing a for loop:

1. Traverse a sequence to extract some information

2 .Generate another sequence from the current sequence

3.Writing for loops is second nature to me because I am a programmer

Fortunately, Python has There are great tools to help you achieve these goals! All you need to do is change your mind and see things from a different perspective.

What will you gain by not writing for loops everywhere

1. Fewer lines of code

2. Better code readability

3. Only use indentation to manage code text

Let's see the code skeleton below:

Look at the structure of the code below:

# 1
with ...:
    for ...:
        if ...:
            try:
            except:
        else:

This example uses multiple levels of nested code, which is very difficult to read. I noticed in this code that it uses indentation indiscriminately to mix management logic (with, try-except) and business logic (for, if). If you adhere to the convention of only using indentation for administrative logic, then the core business logic should be taken out immediately.

“扁平结构比嵌套结构更好” – 《Python之禅》

To avoid for loops, you can use these tools

1. List comprehension/generator expression

Look at a simple example, This example mainly compiles a new sequence based on an existing sequence:

result = []
for item in item_list:
    new_item = do_something_with(item)
    result.append(item)

If you like MapReduce, you can use map, or Python's list analysis:

result = [do_something_with(item) for item in item_list]

Similarly, if If you just want to get an iterator, you can use a generator expression with almost the same syntax. (How could you not fall in love with Python's consistency?)

result = (do_something_with(item) for item in item_list)

Function

Think about it in a higher-order, more functional way, if you want to map a sequence to Another sequence calls the map function directly. (List comprehensions can also be used instead.)

doubled_list = map(lambda x: x * 2, old_list)

If you want to reduce a sequence to one element, use reduce

from functools import reduce
summation = reduce(lambda x, y: x + y, numbers)

In addition, a large number of built-in functions in Python can consume iterators :

>>> a = list(range(10))
>>> a
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> all(a)
False
>>> any(a)
True
>>> max(a)
9
>>> min(a)
0
>>> list(filter(bool, a))
[1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> set(a)
{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
>>> dict(zip(a,a))
{0: 0, 1: 1, 2: 2, 3: 3, 4: 4, 5: 5, 6: 6, 7: 7, 8: 8, 9: 9}
>>> sorted(a, reverse=True)
[9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
>>> str(a)
'[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]'
>>> sum(a)
45

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