Python Tips

Python takes some getting used to. The clean syntax is great, but it has some things which a Java or Ruby programmer might not guess.

Problem with deadline after upgrade

When starting python you get an IO error: <geshi lang="bash"> $ python Python 2.6.7 (r267:88850, Feb 3 2012, 20:21:47) [GCC 4.2.1 Compatible Apple Clang 3.0 (tags/Apple/clang-211.12)] on darwin Type "help", "copyright", "credits" or "license" for more information. /Users/brianegge/.pyhistory Traceback (most recent call last):

 File "/Users/brianegge/.pystartup", line 24, in <module>
   readline.read_history_file(historyPath)

IOError: [Errno 2] No such file or directory >>> </geshi>

Your ~/.pystartup looks like: <geshi lang="python"> import atexit import os import readline import rlcompleter

historyPath = os.path.expanduser("~/.pyhistory")

def save_history(historyPath=historyPath):

   import readline
   readline.write_history_file(historyPath)

if os.path.exists(historyPath):

   readline.read_history_file(historyPath)

</geshi>

The solution is to remove your old history file rm /Users/brianegge/.pyhistory

After you run python again, you will see new magic at the top of your readline file: <geshi lang="bash"> cat ~/.pyhistory _HiStOrY_V2_ </geshi>

How to tell if an object is None

This won't parse: <geshi lang="python"> user = users.get_current_user() if !user:

   gologin()

</geshi>

This works: <geshi lang="python"> if not bool(user):

   gologin()

</geshi>

As does: <geshi lang="python"> if user == None:

   gologin()

</geshi>

But this is probably best: <geshi lang="python"> if user is None:

   gologin()

</geshi>

This article "what exactly is "None"" helped explain this a little better.