python - 为什么当我正确缩进打印行时终端中出现语法错误消息，但当我缩进它时程序运行并打印输出 33 次？

Question

fname = input('Enter the file name:')
Enter the file name:mbox-short.txt
>>> fhand = open(fname)
>>> count = 0
>>> for line in fhand:
...     if line.startswith('Subject:'):
...         count = count + 1
... print('There were', count, 'subject lines in', fname)
  File "<stdin>", line 4
    print('There were', count, 'subject lines in', fname)
    ^
SyntaxError: invalid syntax
>>> 

一开始我用的是制表符，但是不一致，所以我用了空格，数得很仔细。然后我尝试使用 Enter 键而不是 Return 键。然后我缩进了 print 语句，程序运行了，但是输出很古怪:

There were 0 subject lines in mbox-short.txt
There were 0 subject lines in mbox-short.txt
There were 0 subject lines in mbox-short.txt....to 
There were 27 subject lines in mbox-short.txt
There were 27 subject lines in mbox-short.txt
There were 27 subject lines in mbox-short.txt

这从第 0 行开始，每行每个数字打印大约 30 次。我想不出任何其他方法来尝试消除不允许我以正确的缩进运行 print 语句的语法错误。如果这对有经验的程序员来说显而易见，我深表歉意，但我们将不胜感激任何有用的提示。

Answer 1

当您使用交互式解释器时，您需要在缩进 block 的末尾包含一个空行，然后才能继续执行该程序。这只是交互式环境的一个怪癖，您的代码可以在 .py 文件中正常工作。

因此，您的 session 应如下所示:

>>> fname = input('Enter the file name:')
Enter the file name:mbox-short.txt
>>> fhand = open(fname)
>>> count = 0
>>> for line in fhand:
...     if line.startswith('Subject:'):
...         count = count + 1
... 
>>> print('There were', count, 'subject lines in', fname)