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，就用空格，算的很仔细。然后我尝试使用 Enter 键而不是 Return 键。然后我缩进打印语句和程序运行，但输出很古怪：

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运行具有正确缩进的 print 语句的语法错误。如果这对有经验的程序员来说很明显，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，您需要在缩进块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，您的代码在 .py 文件中可以正常工作。

因此，您的会话应如下所示：

>>> 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)

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？

Why a syntax error message in Terminal when I indent the print line correctly, yet the program runs and prints the output 33 times when I indent it?

python

syntax