python - 在完全嵌套的 for 循环中返回值

Question

我想要嵌套循环来测试所有元素是否匹配条件，然后返回 True。示例:

有一个给定的文本文件:file.txt，其中包含以下模式的行:

aaa:bb3:3

fff:cc3:4

字母、冒号、字母数字、冒号、整数、换行符。

一般来说，我想测试所有行是否都匹配这个模式。但是，在此函数中，我想检查第一列是否仅包含字母。

def opener(file):
    #Opens a file and creates a list of lines
    fi=open(file).read().splitlines()
    import string
    res = True
    for i in fi:
        #Checks whether any characters in the first column is not a letter
        if any(j not in string.ascii_letters for j in i.split(':')[0]):
             res = False
        else:
            continue
    return res

但是，即使第一列中的所有字符都是字母，该函数也会返回 False。我也想请你解释一下。

Answer 1

您的代码评估代码后面的空行 - 因此False:

您的文件在最后一行之后包含换行符，因此您的代码会检查最后一个数据之后的行，但该行未满足您的测试 - 这就是为什么无论输入如何，您都会得到False:

aaa:bb3:3
fff:cc3:4
                    empty line that does not start with only letters

如果您“特殊处理”空行(如果它们出现在末尾)，则可以修复它。如果填充行之间有空行，您也会返回 False:

with open("t.txt","w") as f:
    f.write("""aaa:bb3:3
fff:cc3:4
""") 

import string 
def opener(file):
    letters = string.ascii_letters
    # Opens a file and creates a list of lines
    with open(file) as fi:
        res = True
        empty_line_found = False
        for i in fi:
            if i.strip(): # only check line if not empty
                if empty_line_found:  # we had an empty line and now a filled line: error
                    return False
            #Checks whether any characters in the first column is not a letter
                if any(j not in letters for j in i.strip().split(':')[0]):
                    return False   # immediately exit - no need to test the rest of the file
            else:
                empty_line_found = True

    return res # or True


print (opener("t.txt"))

输出:

True

<小时/>

如果你使用

# example with a file that contains an empty line between data lines - NOT ok
with open("t.txt","w") as f:
    f.write("""aaa:bb3:3

fff:cc3:4
""") 

或

# example for file that contains empty line after data - which is ok
with open("t.txt","w") as f:
    f.write("""aaa:bb3:3
ff2f:cc3:4


""") 

你得到:False