从python 3.x中的文件读取输入 [英] Reading input from a file in python 3.x

问题描述

假设您正在从结构类似的文件中读取输入

Say you are reading input from a file structured like so

P3
400 200
255
255 255 255
255 0 0
255 0 0
etc...

但是您要考虑输入文件中可能出现的任何错误，如

But you want to account for any mistakes that may come from the input file as in

P3 400
200
255
255 255
255
255 0 0
255 0
0
etc...

我想读第一个令牌"P3"，然后读下两个"400"，"200"(高度/宽度)"255"，从这里开始，我想读入每个令牌并说明它们的方式应该以3为一组.我具有读取此信息的正确代码，但似乎无法弄清楚如何通过令牌而不是逐行读取信息.

I want to read in the first token 'P3' then the next two '400' '200' (height/width) the '255' and from here on, I want to read every token in and account for how they should be in groups of 3. I have the correct code to read this information but I can't seem to get past the wall of figuring out how to read in information by token and not by line.

没有考虑输入不正确的情况.

Which doesn't account for an imperfect input.

推荐答案

如果您的文件由三个值组成的组(在第一个P3项之后)，并且您不能依靠换行符将它们正确分组，我建议将文件作为单个字符串读取，然后进行拆分和分组.这是简单明了的方法:

If your file consists of groups of three values (after the first P3 item) and you cannot rely upon the line breaks to have them grouped properly, I suggest reading the file as a single string and doing the splitting and grouping yourself. Here's a straight-forward way:

with open(filename) as f:
    text = f.read()    # get the file contents as a single string

tokens = text.split()  # splits the big string on any whitespace, returning a list
it = iter(tokens)      # start an iterator over the list
prefix = next(it)      # grab the "P3" token off the front
triples = list(zip(it, it it))  # make a list of 3-tuples from the rest of the tokens

在同一引用的多个引用上使用zip是这里的关键.如果需要使用相同的代码处理其他组大小，则可以使用zip(*[it]*grouplen).

Using zip on multiple references to the same iterator is the key trick here. If you needed to handle other group sizes with the same code, you could use zip(*[it]*grouplen).

请注意，这将丢弃文件末尾的所有剩余值(如果它们不是三个组成的一组).如果您需要以不同的方式处理这种情况，建议您使用itertools模块中的zip_longest，而不是常规的zip函数. (请参见 itertools文档中的grouper食谱 )

Note that this will discard any left-over values at the end of the file if they don't form a group of three. If you need to handle that situation differently, I suggest using zip_longest from the itertools module, rather than the regular zip function. (See the grouper recipe in the itertools documentation.)

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