英文:
Why does a for loop work inside of a list
问题
我试图理解这行代码的工作原理，但没有成功。
x, y = [float(num) for num in input("输入一个点：").split(",")]
我尝试将这段代码分成几个部分，但这并没有解释这行代码的工作方式。
英文:
I'm trying to understand how this line of code works but to no luck.
x, y = [float(num) for num in input("Enter a point: ").split(",")]
I did try to split this code in sections but that didn't explain how this line of code worked
答案1
得分: 2
Sure, here's the code part you provided in Chinese:
tmp_list = [] # 创建一个临时列表来保存分割的输入
point = input("输入一个点：") # 获取数据
for num in point.split(","): # 在逗号上分割字符串，然后迭代
tmp_list.append(float(num)) # 将每个值转换为浮点数并添加到列表
x, y = tmp_list # 解包列表为x和y。这假设列表始终长度为2
del tmp_list # 删除临时列表
英文:
You could break the code out as (see comments):
tmp_list = [] # create a temporary list to hold split input
point = input("Enter a point: ") # get the data
for num in point.split(","): # split string on comma then iterate
tmp_list.append(float(num)) # make a float from each value and append to list
x, y = tmp_list # unpack list to x,y. This assumes list is always len 2
del tmp_list # delete temporary list
答案2
得分: 1
这是一种称为列表推导的方法。它在Python中用于缩短从另一个列表创建列表的代码。让我们一步一步来。
[float(num) for num in input("输入一个点：").split(",")]
首先，我们看到列表推导本身，作为for num in ...，但它正在迭代什么？它正在迭代一个输入函数，由逗号分隔。split方法将一个字符串按给定的分隔符拆分并返回一个列表。这就是在列表推导中进行迭代的内容。然后，代码将该字符串值转换为浮点数，然后通过解包返回的列表传递给x和y变量。
本质上，这是一种大量简化了@tdelaney答案中的代码的语法糖。
英文:
This is a method known as list comprehension. It is used in python to shorten code that creates a list from another list. Let's go step by step.
[float(num) for num in input("Enter a point: ").split(",")]
First, we see the comprehension itself, as for num in ..., but what is it iterating over? It iterates over an input function, split by a comma. The split method will split a string by the given seperator and return a list. This is what is being iterated over in the comprehension. The code then converts that string value into a float, before passing it on to the x and y variables by depacking the list returned
In essence, this is a lot of syntactic sugar that shortens the code in @tdelaney's answer
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