On: Don’t Slurp: How to Read Files in Python

[riskable]

His example is OK but I was able to improve it significantly with a few minor changes:

    "A simple filter that prepends line numbers" # <-- Docstring
    import sys
    for fname in sys.argv[1:]: # ./program.py file1.txt file2.txt ...
        with open(fname) as f:
            # This reads in one line at a time from stdin
            for lineno, line in enumerate(f, 1): # Start at 1
                print '{:>6} {}'.format(lineno, line[:-1])

My way lets you pass as many files as you want to stdin, has a proper docstring, and uses the enumerate() function (so you don't need the silly `lineno = 0` and `lineno += 1` lines).

[fredsanford → riskable]

And yours doesn't work with stdin...

What's with all the nitpicking?

[nobodysfool → riskable]

nah, way better to use a generator...

    with open("a.txt") as f:
        c = ["{0} : {1}".format(x,y) for x,y in enumerate(f,1) ]
    for x in c:
        print x,

[prutschman → nobodysfool]

c is assigned a list, not a generator. Switching the square brackets for parenthesis creates a generator, but attempting to access the elements will fail because f was closed after exiting the 'with' scope.

  <ipython-input-8-e2c5ebe72b17> in <module>()
  ----> 1 for x in c:
        2     print x,
        3 
  
  <ipython-input-7-9460e3a04a4e> in <genexpr>(***failed resolving arguments***)
        1 with open("/tmp/foo.txt") as f:
  ----> 2     c = ("{0} : {1}".format(x,y) for x,y in enumerate(f,1))
        3 
  
  ValueError: I/O operation on closed file