Difference between revisions of "Python"

Revision as of 20:30, 2 April 2011

HRL Coding Standards

In general, we strongly recommend that everyone follow the official python coding standards (Python standards) but we will summarize here the relevant key points.

• Every indent is 4 spaces, replace all tabs with spaces.
• Don't use 'from blah_module import *'
• imported names must be longer than 1 character.
• all imports should be at the top of your file except for..
• imports that are only used in your __main__ blocks should be at the beginning of that __main__ block.
• ClassName, method_name, _private_name
• Use default parameters sparingly.
• Use classes sparingly, please try to define functions whenever possible. Functions should not be more than a page or two long unless there is an extremely good reason to do so.
• Instead of using inheritance, use duck typing (i.e. define interfaces based on conventions)
• With numpy, use matrices instead of arrays, all vectors should be column vectors.
• Debugging printouts that are left in the code should be annotated with the class and method name that is generating it. Instead of:

 def some_func(a,b):
   print "results of a + b", a+b

Use:

 def some_func(a,b):
   print "<my_file.py> some_func: results of a+b

• We use doxygen styled comments:

 ##
 # some comments
 # @param a is 3x1 point in coordinate frame C
 # @param b is a 3x3 rotation matrix
 # @return a 3x1 vector rotated by b
 def my_function(a, b):
     return b*a

• Use whitespace to separate functional parts of code, but do not use them misleadingly. This is misleading:

       self.size_image = highgui.cvQueryFrame(self.capture)
       self.size = cv.cvGetSize( self.size_image )

       self.color = cam_param['color']

       self.intrinsic_cvmat = cv.cvCreateMat(3,3,cv.CV_32FC1)
       self.distortion_cvmat = cv.cvCreateMat(1,4,cv.CV_32FC1)

The below would be preferred if there are not obvious separations:

       self.size_image = highgui.cvQueryFrame(self.capture)
       self.size = cv.cvGetSize( self.size_image )
       self.color = cam_param['color']
       self.intrinsic_cvmat = cv.cvCreateMat(3,3,cv.CV_32FC1)
       self.distortion_cvmat = cv.cvCreateMat(1,4,cv.CV_32FC1)

• Again, we strongly recommend that you be extremely familiar with the python coding standards: Python standards

learning python

• We use python 2.5.2 and code using the Python coding standards.
• http://docs.python.org/
• http://docs.python.org/library/index.html
• python for programmers
• guido's guide (http://docs.python.org/tut/)
• dive into python (book) (http://www.diveintopython.org/toc/index.html)
• quick reference (http://rgruet.free.fr/PQR25/PQR2.5.html)
• ipython (http://ipython.scipy.org/moin/)
  • to execute a scriot in ipython, type: run [script name]

math, science, numerical, etc.

• numpy (http://numpy.scipy.org/)
• scipy (http://scipy.org/)
• matplotlib (http://matplotlib.sourceforge.net/): in ipython shell
• mayavi (http://code.enthought.com/projects/mayavi/)

opencv

• python specific documentation: PythonInterface, SWIG Python Interface

efficiency

• When you need buffering of some sort for logging/writing data, if speed is important use the deque data structure instead of lists: http://docs.python.org/library/collections.html#collections.deque