Python is a convenient language that’s often used for scripting, data science, and web development.
In this article, we’ll look at how to define and use modules to separate large programs into small pieces.
Most programs are more than a few lines long. This means that they have to split into multiple small pieces for them to be manageable.
Python programs can be split into modules. Each module is a Python program. For example, the
math module has math functions and the
random module has random number-related functions.
To use Python modules in another module, we have to use the
import keyword and the name of the module.
If we want to import more than one module, we can separate the module names by commas.
For example, we can import the
random module and then print out a randomly generated number by calling the
randrange function as follows:
import random print(random.randrange(0, 101, 2))
In the code above, we import the
random module and called the
randrange function with the start and end numbers of the number we want to generate as the first 2 arguments.
The end number is excluded from the range of numbers that can be generated.
The last argument has the number of steps to skip between the start and end numbers.
The code above will generate an even number in the range of 0 to 100 inclusive.
from import Statements
We can just import one member of a Python module with the
For example, we can just import the
randrange function from the
random module as follows:
from random import randrange print(randrange(0, 101, 2))
In the code above, we just import the
randrange function instead of the whole module.
But the rest of the logic is the same.
This is more efficient since we didn’t import everything.
Create Our Own Modules
Anything that is at the top level of a Python file can be imported from a Python module.
For example, we can create a module called
foo.py as follows:
x = 1
main.py , we can import and use it as follows:
import foo print(foo.x)
We should see 1 on the screen since we have
x set to 1 and imported it.
The Module Search Path
Python modules are searched in the code directory, the path set as the value of the
PYTHONPATH environment variable, and the default directory that’s set when Python is installed.
dir function is used to list the members of a Python module.
For example, we can print a list of members of the
math module as follows:
import math print(dir(math))
Then we get the following on the screen:
['__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__', 'acos', 'acosh', 'asin', 'asinh', 'atan', 'atan2', 'atanh', 'ceil', 'copysign', 'cos', 'cosh', 'degrees', 'e', 'erf', 'erfc', 'exp', 'expm1', 'fabs', 'factorial', 'floor', 'fmod', 'frexp', 'fsum', 'gamma', 'gcd', 'hypot', 'inf', 'isclose', 'isfinite', 'isinf', 'isnan', 'ldexp', 'lgamma', 'log', 'log10', 'log1p', 'log2', 'modf', 'nan', 'pi', 'pow', 'radians', 'remainder', 'sin', 'sinh', 'sqrt', 'tan', 'tanh', 'tau', 'trunc']
We can see the functions that we can call from the array above.
We can put Python files in directories to organize them into packages.
For example, we can put
foo.py in the
package folder, add
__init__.py to it.
Then we can import and use package’s members as follows:
from package import foo print(foo.x)
Importing * From a Package
The asterisk character indicates that we import all the members from a package.
For example, if we write:
from sound.effects import *
we import all the members from the
effects module in the
This is bad practice because the code is inefficient because we import everything. Also, we may have clashing names since we import more members than we’re supposed to.
We can use the
as keyword to import a module with an alias name. This helps us avoid clashes of names from different modules where we have members that have the same name in different modules.
For example, we can write the following code:
import random as r print(r.randrange(0, 101, 2))
to import the
random module with an alias
r and reference that instead of
We can also import a member with as an alias as follows:
from random import randrange as rr print(rr(0, 101, 2))
We can call
rr instead of
randrange to call
We can define and import Python modules by creating a Python code file and then we can import the members of the Python file.
This lets us divide code into small pieces.
Also, we can organize Python modules into packages by putting module files in folders and add
__init__.py to each directory.