Retrieving number of lines with python

Question

I am trying to retrieve the number of lines of a file using python on ubuntu.

I tried the following:

os.system("wc -l fileName")

But it returns something like

numberOfLines fileName
0

When I tried to retrieve the result: l = os.system("wc -l fileName")

I got l = 0

I also tried to split the result in order to keep the first element only, but this raises AttributeError: 'int' object has no attribute 'split'

How can I get the number of lines I am looking for?

possible duplicate of How to get line count cheaply in Python? — pseudocubic
– pseudocubic, Commented Mar 7, 2014 at 14:32

w-m · Accepted Answer · 2014-03-07 14:42:23Z

3

os.system will return the exit value of the wc -l command, which is zero if no error occurs.

You want the actual output of the program:

#TODO: handle CalledProcessError, malformatted output where appropriate

wc_output = subprocess.check_output(["wc", "-l", fileName])
num_lines = int(wc_output.split()[0])

edited Mar 7, 2014 at 14:42

answered Mar 7, 2014 at 14:31

w-m

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7 Comments

kojiro Over a year ago

It's worth knowing that wc prints the filename if it's an argument, but not if counting lines from stdin.

bigTree Over a year ago

@w.m Similarly, I tried subprocess.check_output(["ls","files*"]) but got an error telling the file files* doesn't exist. How can I specify that I want all the files whose name begins with files?

kojiro Over a year ago

@w.m er, not that my happiness has anything to do with it, but wouldn't it be better just to redirect the file to stdin for wc, rather than using split?

w-m Over a year ago

@bigTree lookup glob/globbing and maybe the shell=True flag (and its security warnings)

w-m Over a year ago

@kojiro you'd have to open the file in Python or use shell=True though?

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