CODEWITHSUNDEEP
pythonfilegenerator
PedroA
PedroA

Reputation: 1925

Generator to read lines from file

Is there any advantage of using a generator function to read lines from a file? I'm asking this because I saw something like this in a script:

with open(file, 'r') as f:
    liter = (l.rstrip("\r\n") for l in f)  # <generator object <genexpr> at 0x10617c728>
    for line in liter:

Would this approach be better (or in what circumstances) than a simple block like:

with open(file, 'r') as f:
    for line in f:
        line = line.rstrip("\r\n")

Upvotes: 4

Views: 8326

Answers (1)

Jean-Fran&#231;ois Fabre
Jean-Fran&#231;ois Fabre

Reputation: 140186

The first approach doesn't bring much:

  • it is not a full comprehension syntax since there's a loop
  • it is not a full loop code (so beginners will have a hard time understanding it)

It would have an interest if you could write your code in one line without the loop:

result = [x for x in (l.rstrip("\n") for l in f) if x]

(creating a list of non-empty lines, that is, and as a side note, you don't have to strip \r from the end of line because text mode already does it, unless of course there are more than 1 \r character, which is non-standard)

Or in a lambda that you would use all over your code to avoid forgetting removing those damn linefeeds:

stripped_lines = lambda f : (l.rstrip("\n") for l in f)

then

for l in stripped_lines(f):
   ...

The second approach is clearer and simpler if you have to use a loop (if you have side-effect calls, it's recommended to avoid comprehensions and use loops instead)

Upvotes: 4

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