Things about Python that I find cool

Python is a formidable language with functional capabilities that is extraordinarily easy to learn and follow. It is interpreted so that scripting and prototyping are possible.

Commentaries follow UNIX style so that you can use it for building scripts (and therefore program CGIs).

Despite striking as too odd at first sight, Python's syntax overweights its cons by offering a clear and simple look which noticeably increases productivity. Python relies on indentation to define its blocks, which means that you get rid of parentheses, brackets, black keywords such as begind or end, etc. This simplifies code and makes it more readable

for i in vector:
     if i==1:
        print i<<1
     else:
        print i**2
     print "Loop: %d" % i

IPython notebook (which requires Tornado libraries), is an interesting addon over IPython (which itself gives you nice command line ammenities). It is a Javascript/CSS served over a local HTTP server which allows you for nice online prototyping on your web browser. Results are inlined much like a Maple or Mathematica session.

It allows for powerful expressions, such as performing a transformation on filtered data with a near natural language expression:

[x**2 for i, x in enumerate(col) if i!=0 or x]

Here we transform all elements in the vector col squaring them but only those whose index is not zero.

Decorators are a powerful way to add behavior to a function, adding code that performs some task before and after the target function is executed. The canonical use of decorators is adding logging behavior to functions. In Python we can use them easily and non-intrusively by adding the operator @ and the decorator function to the definition of the function

def decorator(func):
    def inner(x):
       print "Arguments were ", x
       y = func(x)
       print "Result is", y
    return innter

The argument operators * and ** allow for generics construction within the functions. By convention, one uses *args for sequential expansion of the argument list and of and **kwargs for named expansion of an argument list. This means that you can use * in the function definition to represent a list of arguments passed in order, therefore *args becomes a list of values that you can then use. On the other hand, calling a function that has named parameters with a list of values with the operator * will result in expanding the values to these arguments.

def test(a=1, b=2):
    print a, b
args=(1,2)
test(*args)
1 2

Similarly, **kwargs cab be used to either specify a list of generic argument list to make the behavior of the function dynamical (for example, your function is a relay and just gets arguments that passes on to other functions that will interpret them), or be used to expand a map of named arguments in this way

def test(a=1, b=2):
    print a, bs
kwargs = {"a":1,"b":2}
test(**kwargs)
1 2

Althoug the following does not refer to the language itself, it has to do with the community, since there exists a service called PyCloud that enables Python practitioners to use CPU power for their Python numerical needs. As per the PyCloud site:

The PiCloud Platform gives you the freedom to develop your algorithms and software without sinking time into all of the plumbing that comes with provisioning, managing, and maintaining servers.

You have 20 free computing hours.

Finally, a powerful and comprehensive set of libraries has been built on Python, especially for Data Analysis: Python probably has the largest collection of opensource libraries for data analysis. It includes: NumPy, SciPy, Pandas, Sklearn, NLTK and many others.