# L-25 MCS 275 Wed 10 Mar 2010 : grabpyhead.py

# Grabs the header line of all .py programs.
# When the file starts with '#!', the header
# line is not the first but the second line.
# Every file has four fields:
# type, number, date, and file name.

import os

def HasPyExt(name):
   """
   Returns True if the name ends in ".py",
   returns False otherwise.
   """
   try:
      if name[-3:] == '.py':
         return True
      else:
         return False
   except:
      return False

def StartPath(line):
   """
   Returns True if the line appears to be
   the path of the python interpreter,
   returns False otherwise.
   """
   try:
      if line[0:2] == '#!':
         return True
      else:
         return False
   except:
      return False

def SplitFields(line):
   """
   Returns a tuple with the fields of the header.
   """
   L0 = line.split(' : ')
   fname = L0[1]
   L1 = L0[0].split(' MCS 275 ')
   fdate = L1[1]
   L2 = L1[0].split(' ')
   L3 = L2[1].split('-')
   ftype = L3[0]
   fnumb = L3[1]
   return (ftype,fnumb,fdate,fname)

def EnumFields(d,f):
   """
   Enumerates all fields in the header of
   the .py files in the directory d.
   For each field, the function f is called.
   Returns the number of .py files.
   """
   L = os.listdir(d)
   cnt = 0
   for filename in L:
      if HasPyExt(filename):
         cnt = cnt + 1
         file = open(filename,'r')
         s = file.readline()
         if StartPath(s): s = file.readline()
         try:
            f(SplitFields(s[:-1])) # omit \n
         except:
            print 'exception occured with file ' + filename
      file.close()
   return cnt

def PrintFields(s):
   """
   Use as argument to test the enumerator.
   """
   print s

def main():
   """
   Prints the header of all .py files
   in the current directory.
   """
   n = EnumFields('.',PrintFields)
   print 'counted %d .py files' % n

if __name__ == "__main__": main()