On Tue, Aug 7, 2018 at 11:16 PM Ken Hilton <kenlhil...@gmail.com> wrote:
> ...
> Now, let's take a look at the following scenario:
>
> def read_multiple(*filenames):
> for filename in filenames:
> with open(filename) as f:
> yield f.read()
>
> Can you spot the problem? The "with open(filename)" statement is supposed
> to ensure that the file object is disposed of properly. However, the "yield
> f.read()" statement suspends execution within the with block, so if this
> happened:
>
> for contents in read_multiple('chunk1', 'chunk2', 'chunk3'):
> if contents == 'hello':
> break
>
> and the contents of "chunk2" were "hello" then the loop would exit, and
> "chunk2" would never be closed! Yielding inside a with block, therefore,
> doesn't make sense and can only lead to obscure bugs.
>
Instead of disallowing code, this is a case for allowing with expressions:
def read_multiple(*filenames):
for filename in filenames:
yield (f.read() with open(filename) as f)
Elazar
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