Packages, functions, and modules

An important part of coding (in Python and in other modern language) is organizing code in easily re-used chunks.

Python can work within both a procedural and an object-oriented style.

Procedural programming uses functions

Object oriented uses classes. Today we'll discuss procedural, next week we'll discuss object oriented programming.

What is a function?



In [7]:

    
def fizzbuzz(ntot, show=True):
    pass

You can name your function anything, as long as it doesn't start with a number, isn't a built-in keyword, and only contains numbers, letters, and underscores

Note for IDL users: there is no difference between functions and procedures. All Python functions return a value: if no return is specified, it returns None



In [10]:

    
def addnums(x, y=3):
    return x + y



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addnums(2, 4)









    Out[11]:





6



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addnums(5)









    Out[13]:





8



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addnums("A", "B")









    Out[14]:





'AB'

Python functions use local variables, unless you use the global variable definition

Documentation rocks, too!



In [15]:

    
def power_of_difference(x, y, p=2.0):
    """Return the power of the difference of x and y
    
    Parameters
    ----------
    x, y : float
        the values to be differenced
    p : float (optional)
        the exponent (default = 2.0)
    
    Returns
    -------
    result: float
        (x - y) ** p
    """
    diff = x - y
    return diff ** p

power_of_difference(10.0, 5.0)









    Out[15]:





25.0



In [16]:

    
help(power_of_difference)









    



Help on function power_of_difference in module __main__:

power_of_difference(x, y, p=2.0)
    Return the power of the difference of x and y
    
    Parameters
    ----------
    x, y : float
        the values to be differenced
    p : float (optional)
        the exponent (default = 2.0)
    
    Returns
    -------
    result: float
        (x - y) ** p



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import mymodule



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import mymodule as m



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from mymodule import *



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from mymodule import add_numbers

Common modules that are useful! numpy, scipy, matplotlib, astropy, pyfits, pandas, scikit-learn

Plotting freestyle time. We'll discuss numpy arrays, and then plot up a vs e from the asteroids table, and talk about some of the basics and import things in numpy and scipy.

Making nice looking code: "code is read much more often than it is written"

The official rules are PEP-0008: https://www.python.org/dev/peps/pep-0008. This is the "The Elements of Style" for Python!

You should read this. In general, white space is a good thing, lines should have a finite width (79 characters), and comments are good to have! You'll often find yourself needing code that you wrote >2 years ago, and it's a bad thing if it takes you longer to understand the code than it would to re-write it from scratch!



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