Question

I have a new problem with a python script. When I try to run it passing a path as argument to the program it returns the error message: “No such file or directory“. The program is supposed to iterate through a directory specified by the path name to look for textfiles and print out the first two lines.

Yes indeed, it is homework, but I have looked and read alot about os and sys but still don’t get it. Can some of you veterans please help a newbie? Thanks

    #!/usr/bin/python2.7
    #print2lines.py
    """
    program to find txt-files in directory and
    print out the first two lines
    """
    import sys, os

    if (len(sys.argv)>1):
        path = sys.argv[0]
        if os.path.exist(path):
            abspath = os.path.abspath(path):
                dirlist = os.listdir(abspath)
                for filename in dirlist:
                    if (filename.endswith(".txt")):
                        textfile = open(filename, 'r')
                        print filename + ": \n"
                        print textfile.readline(), "\n"
                        print textfile.readline() + "\n"

                    else:   
                        print "passed argument is not valid pathname"
    else:   
        print "You must pass path to directory as argument"

Answer 1

os.listdir returns a list of the names of files in the directory, but not their path. E.g. you have a directory ‘test’ and files a,b and c in it:

os.listdir("test") #-> returns ["a", "b", "c"]

if you want to open the files, you need to use the full path:

from os import path, listdir
def getpaths(dirname):
    return [path.join(dirname, fname) for fname in listdir(dirname)]
getpaths("test") #-> returns ["test/a", "test/b", "test/c"]

the full solution to your problem in five lines:

import sys, os
dir = sys.argv[1]
files = [open(os.path.join(dir, f)) for f in os.listdir(dir)]
first2lines = ['\n'.join(f.read().split("\n")[:2]) for f in files]
print '\n'.join(first2lines)