Group items tagged

def PreOrder(self): print self.data if self.left: print self.left.PreOrder() if self.right: print self.right.PreOrder()

*name must occur before **name.

keys = sorted(keywords.keys()) for kw in keys: print kw, ":", keywords[kw]

Note that the list of keyword argument names is created by sorting the result of the keywords dictionary’s keys() method before printing its contents; if this is not done, the order in which the arguments are printed is undefined

usually __iter__() just return self if you have already define the next() method (generator object)

While you are looking at the collections module, consider inheriting from Sequence, Mapping or another abstract base class if that is more appropriate. Here is an example for a Sequence subclass:

if hasattr(self.data[0], "__iter__": return self.data[0].__iter__() return self.data.__iter__()

Or in C# using Automatic Properties with compiler generated backing fields: public class Pet { public PetName Name { get; set; } public Person Owner { get; set; } }

it is advised to somehow mix together (e.g. using exclusive or) the hash values for the components of the object that also play a part in comparison of objects.

If a class does not define a __cmp__() or __eq__() method it should not define a __hash__() operation either

Called when an attribute lookup has not found the attribute in the usual places (i.e. it is not an instance attribute nor is it found in the class tree for self). name is the attribute name. This method should return the (computed) attribute value or raise an AttributeError exception.

common ways to use doctest: To check that a module’s docstrings are up-to-date by verifying that all interactive examples still work as documented. To perform regression testing by verifying that interactive examples from a test file or a test object work as expected. To write tutorial documentation for a package, liberally illustrated with input-output examples. Depending on whether the examples or the expository text are emphasized, this has the flavor of “literate testing” or “executable documentation”.

Running the module as a script causes the examples in the docstrings to get executed and verified

The file content is treated as if it were a single giant docstring; the file doesn’t need to contain a Python program! For example, perhaps example.txt contains this

mixin class

Another issue with the __dict__ comparison is what if you have an attribute that you don't want to consider in your definition of equality (say for example a unique object id, or metadata like a time created stamp).

isinstance sucks

Re: Python : map and filter vs for loops The underlying implementation of map and filter are different than loops, even though they accomplish the same thing. Which idiom runs fastest can change from version to version. Right now I think list comprehensions are the fastest. So instead of Code: filter(f, range(2,25)), the list comprehension would be Code: [x for x in range(2,25) if f(x)] and instead of Code: map(cube, range(1, 11)) the list comprehension would be Code: [cube(x) for x in range(1,11)]

gevent is a coroutine-based Python networking library that uses greenlet to provide a high-level synchronous API on top of the libev event loop. Features include: Fast event loop based on libev (epoll on Linux, kqueue on FreeBSD). Lightweight execution units based on greenlet. API that re-uses concepts from the Python standard library (for example there are Events and Queues). Cooperative sockets with SSL support » DNS queries performed through threadpool or c-ares. Monkey patching utility to get 3rd party modules to become cooperative »

ActiveState research Python for .NET is a near-seamless integration of the CPython runtime with the .NET Common Language Runtime (CLR). IronPython is an implementation of Python for .net, which allows you to import .net class libraries seamlessly in Python.

This article is about a Python library I created to manage binary search trees. I will go over the following: Node class Insert method Lookup method Delete method Print method Comparing 2 trees Generator returning the tree elements one by one

https://laurentluce@github.com/laurentluce/python-algorithms.git

binary search tree

The Dependency Injection (DI) is an essential pattern when building large systems. It forces classes to be more modular and reusable by making them depend on an interface instead of a concrete class. Simply put classes favor instances passed into the init instead of creating new instances.

Comprehensions are just a simple form of iterators. Generators are just a simple form of iterators

The first argument of every class method, including the __init__() method, is always a reference to the current instance of the class. By convention, this argument is named self.

self is not a reserved word in Python, merely a naming convention

x << yReturns x with the bits shifted to the left by y places (and new bits on the right-hand-side are zeros). This is the same as multiplying x by 2**y.

x >> yReturns x with the bits shifted to the right by y places. This is the same as //'ing x by 2**y.

x & yDoes a "bitwise and". Each bit of the output is 1 if the corresponding bit of x AND of y is 1, otherwise it's 0.

a if test else b

a well defined mental model of the problem domain

Refining the architecture is part of the "refactor mercilessly" rule

If you've never inherited from a built-in data type, experiment with a small test case in a throw away script. This way you don't mangle your current project and you can be as experimental as you like.

if A: will call A.__nonzero__()

and so A is not None is faster since there is much less work to do

if A: seems to be more efficient

The FOX toolkit is an open source, cross-platform widget toolkit, that is, a library of basic elements for building a graphical user interface (GUI). FOX stands for Free Objects for X.

FOX differentiates itself in the following way from other cross-platform toolkits: Tk is a cross-platform toolkit but does not have all of the widgets that FOX considers desirable. Qt had a different licensing model, which might have required a commercial license in some cases where FOX would not. (This is no longer the case starting with Qt 4.5.) wxWidgets promotes the use of native widgets on each supported platform. FLTK is a fast, low-footprint library that supports rapid application development, and requires less code to use, but lacks advanced widgets. All of these toolkits have some support for programming natively on Mac OS and/or Mac OS X platforms, which FOX currently does not support[

The Boost Python Library is a framework for interfacing Python and C++. It allows you to quickly and seamlessly expose C++ classes functions and objects to Python, and vice-versa, using no special tools -- just your C++ compiler. It is designed to wrap C++ interfaces non-intrusively, so that you should not have to change the C++ code at all in order to wrap it, making Boost.Python ideal for exposing 3rd-party libraries to Python. The library's use of advanced metaprogramming techniques simplifies its syntax for users, so that wrapping code takes on the look of a kind of declarative interface definition language (IDL).

The subprocess module allows you to spawn new processes, connect to their input/output/error pipes, and obtain their return codes. This module intends to replace several other, older modules and functions, such as: os.system os.spawn* os.popen* popen2.* commands.*