files.txt
+--

Files

 Files, yes they're on disk, persistent, known to OS.  BUT also...

 Files are a type - have structure and operations

   fd = open('ceru_human.sp')

 Files are iterable: 

   for line in fd:
      print line

 Many things are made to work like files: also processes, web pages, ...

   import os
   pd = os.popen('ls')

   import urllib
   wd = urllib.urlopen('http://staff.washington.edu/jon/')

 Python usually treats different types as similarly as possible 



+--

Exceptions

 Allow recovery from errors, other exceptional conditions

 Exceptions are typical Python style, "easier to ask forgiveness than permission"

 try/except is another control structure like for... or if...

    try:
      fd = open('missing.txt')
    except IOError:
      print "couldn't open missing.txt"

 
  book 14.5 163, better: except IOError  Don't mask other errors!







+--

Operating system functions and scripting

 import sys

 sys.argv is array of strings, command line arguments

 import os

 dir(os)  # many operating system functions

 os.getcwd() # like Unix pwd command
  
 pd = os.popen('ls -l') # run system command and collect output