Python

Modules

Modules are reusable code that can be imported into other scripts or programs. Modules are single files in either .py, .pyc or .pyo format. When a module is imported, code that is not wrapped in a function is executed and the functions themselves are added to the namespace... allowing them to be called upon.

Module Structure

#/usr/lib/python/site-packages/triangle.py

divisor_count_to_find = 500

def triangle_number(n):
    return n*(n+1)/2

def divisors(tn):
    counter = 0
    n_sqrt = int(pow(tn, 0.5))
    for i in range(1, n_sqrt + 1):
        if tn%i == 0:
            counter += 2
    if n_sqrt * n_sqrt == tn:
        counter -= 1
    return counter

def start():
    start_number = 1
    div_numbers = 0
    while (div_numbers < divisor_count_to_find):
        tn = triangle_number(start_number)
        div_numbers = divisors(tn)
        start_number += 1
    print(div_numbers)
    print(tn)

if __name__ == '__main__':
    start()

Reference: if __name__ == '__main__':

In other words, a module is a file containing Python definitions and statements. The file name is the module name with the suffix .py appended (every .py file is a module). Within a module, the module’s name (as a string) is available as the value of the global variable __name__.

Using Modules

• First, we import the module. We will learn more coming up.
• After the module is imported we can begin utilizing the module's objects.
• When a module is imported normally, the module will be on it's own namespace.
  • Thus we need to use dot notation to access the modules objects

import triangle
triangle.start()
triangle.triangle_number(10)
triangle.divisors(10)
triangle.divisor_count_to_find = 100

triangle.start()
# 576 76576500.0 112 73920.0

Importing Modules

There are many ways to import modules. The most common way is to import the module simply using the import keyword alone. These modules are imported from the same dir as your program. This method prevents collisions by putting the modules objects into it's own namespace.

# Most common, clean way to do it. Prevents collisions. 
import triangle
triangle.method # Call method

By default, you cannot import modules from other dirs. You must place your modules in the same dir as your program unless you use sys.path to modify your Python path at runtime. In short, your Python path is where Python searches by default for modules... aside from your current dir.

To add a location to your Python path and runtime:

import sys
sys.path.insert(0, '/path/to/application/app/folder')

import file

There are other methods as well. We can give our modules aliases

# Same as above except we gave triangle an alias
import triangle as tri
tri.method

We can also import specific modules without throwing them into a namespace.

from triangle import divisor_count_to_find, triangle_number

print divisor_count_to_find # output 500
triangle_number(5)

We can take the previous example a step further and implement aliases. This will allow us to change the names up to prevent collisons.

from triangle import divisor_count_to_find as dcf, triangle_number as tn

print dcf # output 500
tn(5)

Lastly, we can also import an entire module without a namespace. The * tells Python to import all modules without a namespace. This is a dangerous method and should only be used if you are sure there will not be collisions.

from triangle import *

Reference: Modules