Scripts and modules

A collection of statements in a file (which usually has a py extension), is called a script. Suppose we put the contents of the following code into a file named smartscript.py:

def f(x):
    return 2*x + 1
z = []
for x in range(10):
    if f(x) > pi:
        z.append(x)
    else:
        z.append(-1)
print(z)

In a Python or IPython shell, such a script can then be executed with the exec command after opening and reading the file. Written as a one-liner it reads:

exec(open('smartscript.py').read())

The IPython shell provides the magic command %run as a handy alternative way to execute a script:

%run smartscript

Simple modules - collecting functions

Often one collects functions in a script. This creates a module with additional Python functionality. To demonstrate this, we create a module by collecting functions in a single file, for example smartfunctions.py:

def f(x):
    return 2*x + 1
def g(x):
    return x**2 + 4*x - 5
def h(x):
    return 1/f(x)

• These functions can now be used by any external script or directly in the IPython environment.
• Functions within the module can depend on each other.
• Grouping functions with a common theme or purpose gives modules that can be shared and used by others.

Again, the command exec(open('smartfunctions.py').read()) makes these functions available to your IPython shell (note that there is also the IPython magic function run). In Python terminology, one says that they are put into the actual namespace.

Using modules and namespaces

Alternatively, the modules  can be imported by the command import. It creates a named namespace. The command from puts the functions into the general namespace:

import smartfunctions
print(smartfunctions.f(2))      # 5

from smartfunctions import g    #import just this function
print(g(1)) # 0
  
from smartfunctions import *    #import all
print(h(2)*f(2))                # 1.0

Tip

Import

The commands import and from  import the functions only once into the respective namespace. Changing the functions after the import has no effect for the current Python session. More on modules can be found in section Modules of Chapter 11, Namespaces, Scopes and Modules.