Request for feedback on my first Python program

[Anand Pillai]

Hi Scott,

   The main problem of your code is in the lines,

   lines = getMeaningfulLines((open(sys.argv[1])).readlines())
   for i in lines:
        print i + " is a ",
        ...
   
   readlines() return lines from the file till the newline character,
   similar to fgets() in C. So what you read in your code is not d:\
   or d:\temp\foo.py but 'd:\<many spaces>\n' and 
   'd:\temp\foo.py<many spaces>\n'.

   To fix this you need to modify the code as follows.

   for i in lines:
        i = string.strip(i) # strip all spaces & newlines
        print i + " is a ",
        ...

   Now your code works correctly.

   Apart from that the main() function can also be defined in 
   the program.

   Here is a modified program with some changes I thought
   made it better.

# scott.py - Scott Meyer's first Effective Python program :-)    
import sys
import os
import string

# Error status codes
BadInvocation = 1

def usage(programName):
    print "Usage: " + os.path.basename(programName) + " [file]"
    sys.exit(BadInvocation)
  
# Take a list of strings, return an equivalent list where the following
# strings have been removed:
# - those with no non-whitespace characters
# - those whose first non-whitespace character is a "#"
def getMeaningfulLines(lines):
    
    nonCommentLines = []
    for line in lines:
        try:
            firstToken = string.split(line)[0]
            if firstToken[0] != "#": 
                nonCommentLines.append(line)
        except IndexError:
            continue
        
    return nonCommentLines
  
def whatami(str):
    
    if os.path.isdir(str): return 'directory'
    elif os.path.isfile(str): return 'file'
    else: return 'non-directory and non-file'

# Here is the main()
def main():
    # if this language had a main(), it'd be here...
    if len(sys.argv) != 2: usage(sys.argv[0])
    
    lines = getMeaningfulLines((open(sys.argv[1])).readlines())
    for i in lines:
        i = string.strip(i)
        print i, 'is a', whatami(i)

if __name__=="__main__":
    main()


Glad to help you pythonically yours,

Anand Pillai

Scott Meyers <Usenet at aristeia.com> wrote in message news:<MPG.194096b51af188bb9896f0 at news.hevanet.com>...
> I'm a C++ programmer who's writing his very first Python program.  This
> means the program is going to be gross, and I apologize for that in
> advance.  I don't really have anybody I can show it to for feedback, so I'm
> hoping I can get some comments here.  If there is a better place for me to
> seek guidance, please let me know.
> 
> The program is supposed to read a file containing directory and file names,
> one per line.  (The file can also contain comment and blank lines, which
> should be ignored.)  For each file or directory name, the program should
> print out whether it's a directory, a file, or neither.  That's it.
> 
> Here's the code; you may want to hold your nose:
> 
>   import sys
>   import os
>   import string
>   
>   # Error status codes
>   BadInvocation = 1
>   
>   def usage(programName):
>     print "Usage: " + os.path.basename(programName) + " [file]"
>     sys.exit(BadInvocation)
>   
>   # Take a list of strings, return an equivalent list where the following
>   # strings have been removed:
>   # - those with no non-whitespace characters
>   # - those whose first non-whitespace character is a "#"
>   def getMeaningfulLines(lines):
>     nonCommentLines = []
>     for i in range(0,len(lines)):
>       try:
>         firstToken = string.split(lines[i])[0]
>         if firstToken[0] != "#": 
>           nonCommentLines.append(lines[i])
>       except IndexError:
>         continue
>     return nonCommentLines
>   
>   
>   # if this language had a main(), it'd be here...
>   if len(sys.argv) != 2: usage(sys.argv[0])
>   
>   lines = getMeaningfulLines(open(sys.argv[1]).readlines())
>   for i in lines:
>     print i + " is a ",
>     if os.path.isdir(i): print "directory"
>     elif os.path.isfile(i): print "file"
>     else: print "non-directory and non-file"
> 
> In addition to the numerious stylistic gaffes I'm sure I've made, the
> program also doesn't work correctly.  Given this input file,
> 
>   d:\
>   d:\temp\foo.py
> 
> I get this output:
> 
>   d:\
>    is a  non-directory and non-file
>   d:\temp\foo.py
>    is a  non-directory and non-file
> 
> Aside from being ugly (how do I get rid of the newline that follows each
> directory or file name?), the problem is that the first entry IS a
> directory and the second one IS a file.  So clearly I'm doing something
> wrong.  Any idea what it is?
> 
> Thanks very much in advance.
> 
> Scott