Python: Difference between revisions

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== Unicode ==
== Unicode ==
;Set source file encoding
Add any of these lines [http://legacy.python.org/dev/peps/pep-0263/]:
<source lang=python>
# -*- coding: utf-8 -*-
# vim: set fileencoding=utf-8 :

</source>

;Write the BOM
;Write the BOM
See [http://stackoverflow.com/questions/934160/write-to-utf-8-file-in-python]
See [http://stackoverflow.com/questions/934160/write-to-utf-8-file-in-python]

Revision as of 17:36, 9 April 2014

Links

  • Nice example of generating / testing regex in Python (with nice / small test framework) [1]

Shell

Use iPy (ipython) to get an interactive shell with auto-completion, instant help...

%magic                    # Get help on %magic commands (%run,...)
?run                      # Get help on %run magic
%run script.py            # Run given script
%run -i script.py         # ... with inspect mode on
%run -i -e script.py      # ... ... and ignore sys.exit() call
!cmd                      # Run shell command 'cmd', for instance ...
!ls                       # ... List file in current directory

Reference

Basic

for i in range(10):
    print i                      # carriage return

for i in range(10):
    print i,                     # no carriage return

Modules

== Tips ==

=== Simple HTTP Server ===
It's very easy to setup an ad-hoc HTTP server with Python. Just open a shell in a folder with some contents to share, and type:

<source lang=bash>
python -m SimpleHTTPServer

More available at http://docs.python.org/2/library/internet.html (see BaseHTTPServer and CGIHTTPServer).

Detect interactive mode

References: [2], [3]

Started with First method Second method Third method Fourth method
import __main__ as main print hasattr(main, '__file__') def in_ipython(): try: __IPYTHON__ except NameError: return False else: return True import sys print hasattr(sys, 'ps1'): import sys print bool(sys.flags.interactive)
python mymod.py True - - -
python -i mymod.py True - - True
python then import mymod - - True -
ipython mymod.py True True - -
ipython -i mymod.py True True - -
ipython then run mymod.py True True - -
ipython then run -i mymod.py True True - -
ipython then import mymod - True - -
ipython -i then import mymod - True - -

Traps

Frequent mistakes. Beware the snake can bite you!

Confuse a method and a property in a test
SOLUTION: Stick to a convention. Like always define methods like isxyyz() or hasabc() as methods. Note that defining them as property would raise an exception if used as a function, and hence might be safer.
if A.isdummy():            # This will fail isdummy is a property
if A.isdummy:              # Always True if isdummy is a method
Mix 0 with None in a sequence
Testing whether an element is defined is more difficult.
a = [0,None,None,None]
bool(a[0])           # --> False
bool(a[1])           # --> False !!! How can we tell them apart?
a[1] == None         # --> True      This works, but is unusual and likely bad practice
Mixing property and normal getter
SOLUTION: prefix all getter method with get, like getvalue()
b = a.prop           # Using a property, OR
b = a.getprop()      # Using a getter


Unicode

Set source file encoding

Add any of these lines [4]:

# -*- coding: utf-8 -*-
# vim: set fileencoding=utf-8 :
Write the BOM

See [5]

import codecs

file = codecs.open("lol", "w", "utf-8")
file.write(u'\ufeff')                          # or use unicode name: u'\N{ZERO WIDTH NO-BREAK SPACE}'
file.close()

# Using https://docs.python.org/2/library/codecs.html#module-encodings.utf_8_sig
with codecs.open("test_output", "w", "utf-8-sig") as temp:
    temp.write("hi mom\n")
Handling unicode

Some recommends to always process unicode internally, and decode on input and encode on output [6]:

line = line.decode('utf-8')
# ...treat line as unicode...
print line.encode('utf-8')

But this is error prone. So another solution proposed is to redefine sys.stdout:

import sys
import codecs
sys.stdout = codecs.getwriter('utf8')(sys.stdout)

An hackish way (not recommended):

# -*- coding: utf-8 -*-
import sys
reload(sys)
sys.setdefaultencoding('utf-8')
print u"åäö"