python中的for循环和zip [英] For loop and zip in python

问题描述

我有一段代码需要理解，我需要帮助.

I have a code that I am trying to understand and I need help.

import numpy as np
Class_numbers=np.array(['a','b','c'])
students_per_class=np.array([10,20,30])
print("Students counts per class:
{}".format(
{x: y for x, y in zip(Class_numbers, students_per_class)}))

输出:

Students counts per class:
{'a': 10, 'b': 20, 'c': 30}

我的理解:1- 我们使用 {} 和 .format(...) 将 {} 替换为 ...

What I understand: 1- we use {} and .format(...) to replace {} with ...

这是我的问题:

Q1- 我不明白对于 x, y in zip(Class_numbers, Students_per_class)".它像一个 2d for 循环吗?为什么我们需要拉链?我们可以有没有 zip 功能的 2d 循环吗?

Q1- I do not understand "for x, y in zip(Class_numbers, students_per_class)". Is it like a 2d for loop? why we need the zip? Can we have 2d loop with out zip function?

Q2-我不明白 x:y 是如何工作的！编译器自动理解 x 和 y 的定义(在x:y"中)在该行的其余部分(例如 for 循环)中进行了描述?

Q2-I am not understanding how x:y works! the compile understand automatically that the definition of x and y (in "x:y") is described in the rest of the line(e.g. for loop)?

P.S:我是 MATLAB 专家，但我是 Python 新手，有时会很困惑！

P.S: I am expert in MATLAB but I am new to python and it is sometimes very confusing!

伊桑

推荐答案

Q1: zip 用于将 2 个列表合并在一起.它返回每个列表的第一个元素，然后是每个列表的第二个元素，依此类推.这是将两个列表视为键和数据以创建字典的技巧.

Q1: zip is used to merge 2 lists together. It returns the first element of each list, then 2nd element of each list, etc. This is a trick to consider the two lists as key and data to create a dictionary.

Q2:这是一个字典(hash)，使用了一种叫做dict comprehension"的方法.它创建显示为输出的字典.如果分配给变量 d、d['a'] = 10 等

Q2: this is a dictionary (hash), using a method called "dict comprehension". It creates the dictionary shown as the output. If assigned to a variable d, d['a'] = 10, etc.

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