[Tutor] More Pythonic?

[Peter Otten]

Timo wrote:

> Op 09-09-15 om 15:41 schreef Steven D'Aprano:
>> On Wed, Sep 09, 2015 at 09:05:23AM -0400, richard kappler wrote:
>>> Would either or both of these work, if both, which is the better or more
>>> Pythonic way to do it, and why?
>> The first works, but isn't really the best way to do it:
>>
>>>   #######################
>>>
>>> import whatIsNeeded
>>>
>>> writefile = open("writefile", 'a')
>>>
>>> with open(readfile, 'r') as f:
>>>      for line in f:
>>>          if keyword in line:
>>>              do stuff
>>>              f1.write(line)
>>>          else:
>>>              f1.write(line)
>>>
>>> writefile.close()
>>>
>>> ######################
>> Better would be this:
>>
>> with open("writefile", 'a') as outfile:
>>      with open("readfile", 'r') as infile:
>>          for line in infile:
>>              if keyword in line:
>>                  do stuff
>>              outfile.write(line)
>>      
> It's also possible to use multiple with statements on the same line. Can
> someone with more expert Python knowledge than me comment on whether
> it's different from using them separate as mentioned by Steven?
> 
> This is what I had in mind:
> 
> with open("writefile", 'a') as outfile, open("readfile", 'r') as infile:
>      pass  # Rest of the code here

This requires Python 2.7 or higher. Other than that the choice is merely a 
matter of taste. Both versions even produce the same bytecode:

$ cat nested_with.py 
def f():
    with open("writefile", 'a') as outfile, open("readfile", 'r') as infile:
        pass  # Rest of the code here

def g():
    with open("writefile", 'a') as outfile:
        with open("readfile", 'r') as infile:
            pass  # Rest of the code here

print(f.__code__.co_code == g.__code__.co_code)
$ python nested_with.py 
True

Personally I find one item per with statement more readable and don't care 
about the extra indentation level.