Python Tips - Revision history

Brianegge at 02:33, 4 February 2012

2012-02-04T02:33:52Z

← Older revision		Revision as of 02:33, 4 February 2012
Line 1:		Line 1:
	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.		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 ==		== How to tell if an object is None ==

Egge at 11:02, 24 September 2008

2008-09-24T11:02:26Z

← Older revision		Revision as of 11:02, 24 September 2008
Line 10:		Line 10:
	</geshi>		</geshi>

	This ~~parses but doesn't work~~:		This works:
	<geshi lang="python">		<geshi lang="python">
	~~user = users.get_current_user()~~		if not bool(user):
	if not user:
	gologin()		gologin()
	</geshi>		</geshi>

	~~This works!~~		As does:
			<geshi lang="python">
			if user == None:
			gologin()
			</geshi>

			But this is probably best:
	<geshi lang="python">		<geshi lang="python">
	~~user = users.get_current_user()~~
	if user is None:		if user is None:
	gologin()		gologin()
	</geshi>		</geshi>

			This article "[http://mail.python.org/pipermail/python-list/2003-March/192769.html what exactly is "None"]" helped explain this a little better.

			[[Category:Python]]

Egge: New page: 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. == How to tell if an object is None == This won't...

2008-09-17T11:12:03Z

New page: 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. == How to tell if an object is None == This won't...

New page

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.

== 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 parses but doesn't work:
<geshi lang="python">
user = users.get_current_user()
if not user:
gologin()
</geshi>

This works!
<geshi lang="python">
user = users.get_current_user()
if user is None:
gologin()
</geshi>