Modules


When we program in Python we basically have 3 main pieces. The base-language itself. A set of standard modules. A set of 3rd party modules.

All the modules provide additional functionality to the base-language and without them we would not be able to do much. The standard modules come installed with Python, the 3rd party modules we need to install. Once installed however they behave in the same way. We need to import them and then we can use them. We'll discuss these even more later, but we already would like to use some so let's see some basic ideas.

I know we already used the math module in the solution of the earlier exercises, but some people might have missed those.

In this example we import the sys module that contains various attributes and operations related to the Python system. (There is another module called os that provides functionality related to the Operating System.)

A few examples:

The executable attribute pointing to where the currently running Python executable is located. On MS Windows this will be a path to a python.exe file.

platform is going to be win32 on any Windows machine.

We are going to discuss the whole sys.argv thing a lot more, but for now look sys.argv[0] contains path to the current Python file.

sys.version_info contains the version information about the currently running Python. Specifically sys.version_info.major contains the major version number which 3 for Python 3 and 2 for Python 2. If really needed, you could use this to recognize when someone is trying to run your program on an unsupported version of Python.

These were all attributes that contain some fixed value.

There is also the getsizeof function that comes with the sys module. You know it is a function because you see a pair of parentheses at the end. The attributes above did not have parentheses. Functions do something. This specific function calculates the number of bytes being used by an object.

You can see an integer (both 1 and 42) use 28 bytes.

A floating point number uses 24 bytes.

An empty string uses 49 bytes.

Then each character takes another byte. (Actually this is only true in the case of latin letters, but let's not get ahead of ourselves.)


examples/basics/modules.py
import sys

print( sys.executable )                 # /home/gabor/venv3/bin/python
print( sys.platform )                   # linux
print( sys.argv[0] )                    # examples/basics/modules.py
print( sys.version_info.major )         # 3

print( sys.getsizeof( 1 ) )             # 28
print( sys.getsizeof( 42 ) )            # 28
print( sys.getsizeof( 1.0 ) )           # 24

print( sys.getsizeof( "" ) )            # 49
print( sys.getsizeof( "a" ) )           # 50
print( sys.getsizeof( "ab" ) )          # 51
print( sys.getsizeof( "abcdefghij" ) )  # 59