Python: Difference between revisions

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{| class=wikitable
{| class=wikitable
|-
|-
!Started with!!First method!!Second method!!Third method
!Started with!!First method!!Second method!!Third method!!Fourth method
|-
|-
|
|
|<source lang=python>
|<source lang=python enclose=none>
import __main__ as main
import __main__ as main
print hasattr(main, '__file__')
print hasattr(main, '__file__')
</source>
</source>
|<source lang=python>
|<source lang=python enclose=none>
def in_ipython():
def in_ipython():
try:
try:
Line 61: Line 61:
return True
return True
</source>
</source>
|<source lang=python>
|<source lang=python enclose=none>
import sys
import sys


if hasattr(sys, 'ps1'):
print hasattr(sys, 'ps1'):
print "Running interactively."
else:
print "Not running interactively..."
</source>
</source>
|<source lang=python>
|<source lang=python enclose=none>
import sys
import sys
print bool(sys.flags.interactive)
print bool(sys.flags.interactive)

Revision as of 13:20, 8 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

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:

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