Using Modules¶

• Functions allow blocks of code to be separated into reusable parts that can be called from a user’s script. Modules take this idea one step further and allow the grouping of functions and code that all perform similar tasks into a library, or in Python speak, module.
• A module has its definitions, the functions and code that make it up, within a separate file ending with a ‘.py’ extension and this file is then imported into a user’s current script. This is most easily demonstrated through an example. We will define a mathematics module called mymath and use this from a separate script.

## File: mymath.py ##
def square(n):
    return n*n

def cube(n):
    return n*n*n

def average(values):
    nvals = len(values)
    sum = 0.0
    for v in values:
        sum += v
    return float(sum)/nvals

• To use this module from a user script we need to tell the script about the module using the import statement. Once the definitions are imported we can then use the functions by calling them as module.functionname. This syntax is to prevent name clashes.

## My script using the math module ##
import mymath  # Note no .py

values = [2,4,6,8,10]
print('Squares:')
for v in values:
    print(mymath.square(v))
print('Cubes:')
for v in values:
    print(mymath.cube(v))

print('Average: ' + str(mymath.average(values)))

• Another variant of the import statement, import``module``as``new-name`` can be used to have the module referred to under a different name, which can be useful for modules with long names

import mymath as mt

print(mt.square(2))
print(mt.square(3))

• It is possible to avoid the module.functionname syntax by using an alternate version of the import statement, from``module``import *. The functions can then be used as if they were defined in the current file. This is dangerous however as you do not have any protection against name conflicts when using multiple modules.

import numpy
print(numpy.__file__)

python
>>> import sys
>>> sys.path.append({Path to mymodule directory})
>>> import mymodule

import datetime as dt
format = '%Y-%m-%dT%H:%M:%S'
t1 = dt.datetime.strptime('2008-10-12T14:45:52', format)
print('Day ' + str(t1.day))
print('Month ' + str(t1.month))
print('Minute ' + str(t1.minute))
print('Second ' + str(t1.second))

# Define todays date and time
t2 = dt.datetime.now()
diff = t2 - t1

Day 12
Month 10
Minute 45
Second 52

import os.path

directory = 'C:/Users/Files'
file1 = 'run1.txt'
fullpath = os.path.join(directory, file1)  # Join the paths together in
                                           # the correct manner

# print stuff about the path
print(os.path.basename(fullpath))  # prints 'run1.txt'
print(os.path.dirname(fullpath))  # prints 'C:\Users\Files'

# A userful function is expanduser which can expand the '~' token to a
# user's directory (Documents and Settings\username on WinXP  and
# /home/username on Linux/OSX)
print(os.path.expanduser('~/test')) # prints /home/[MYUSERNAME]/test on
                                   # this machine where [MYUSERNAME] is
                                   # replaced with the login

import numpy

import numpy
x = numpy.array([1.3, 4.5, 6.8, 9.0])

x = numpy.arange(start=0.0, stop=10.0, step=1.0)

import numpy

x = numpy.array([[1,2,3], [4,5,6], [7,8,9]]) # 3x3 matrix
print(x.ndim) # Prints 2
print(x.shape) # Prints (3L, 3L)
print(x.size) # Prints 9

2
(3, 3)
9

import numpy
a = numpy.array( [20, 30, 40, 50] )
b = numpy.arange( 4 )
c = a-b
print(c)

[20 29 38 47]

x = numpy.array([1,2,3,4,5])
avg = x.mean()
sum = x.sum()
sx = numpy.sin(x)