The day will come when you are stranded in space and need to write a Python script. It’s
unlikely you will have internet access, so if you need help, you’ll be on your own.
To be independent, you need to learn about Python’s interactive help features. With
these, you can quickly learn about classes, modules, functions… Remember, fortune favors
the prepared mind.
To begin, start the Python interpreter…
The first function you need to know is the d-i-r function.
This is short for “directory”.
When you press enter, Python displays a list of available objects. When you first start
the interpreter, there are 4 standard objects. Today we will focus on the first one: built-ins.
This is a module that contains a collection of common objects which are always available
to you. To see the list of built-in objects, view
the directory for the built-ins module. To do this, call the directory function, and
this time pass it the built-ins module name.
This list contains dozens of functions and types ready for use.
To learn about one of these objects, you call the help function with the name of the object.
As an example, let’s learn about the pow function.
This displays the help documentation for the pow function. The first line confirms it is
a function in the built-in module. The following lines show how to use the function.
There are 3 inputs listed: x, y and z. The third input is inside brackets, which means
it is optional. The first two inputs are not inside brackets. That means they are required.
The arrow points to the return type for this function. pow returns a number.
Below the usage is a detailed description of the function.
To test the pow function, let’s raise 2 to the 10th power.
It works! From the description, we see an equivalent way to perform this calculation
is to use a double asterisk.
We get the same answer…
Let’s see another example. First, display the directory of builtin objects.
This time, we will learn about the object called hex. Like before, we will use the
help function.
The first line confirms that hex is a built-in function. You do not need to import anything
to use this function… Next, we see that the input to the hex function is a number,
while the output is a string. Let’s test this function.
The hexadecimal representation of the number 10 is ‘a’.
And that is what we get. Notice that this value is a string, as specified in the help
text. You can tell it is a string because it is surrounded by quotes. Also note that
hexadecimals in Python begin with 0x.
If you ever need to convert a hexadecimal back to a regular decimal, simply type in
the hex value. Be sure to not use quotation marks so Python interprets it as a number,
and not a string.
There are many more modules beyond built-ins. Think of a module as a folder that contains
other Python objects. To see a list of available modules, call help(“modules”).
To learn about a module and see what objects are available, you must first import it. We
will illustrate this by importing the math module…
Once you do this, you can check that it is available to you by calling
the directory function.
See how the math module now appears? It is ready for us to use.
Let’s use the directory function to see what is inside the math module. Call the directory
function with the name of the module. Be careful you do not use quotes. We want the objects
for the module, not a string.
We will investigate the radians function. Watch what happens if we try to display the
help text:
The reason we get a NameError is because the radians function lives inside the math module.
To view the help, you must specify the path to the function: math.radians
We see the function converts degrees to radians. Let’s test this. Recall that 180° equals
π radians.
Once again we got a NameError. The reason is the same as before. We need to specify
the path to the function in order to use it.
It works! Quick note - there is a way to import a function so you do not have to type the
full path. This time-saving feature will be discussed in a separate video on importing
modules.
The next time you are lost in space, don’t panic.
The interactive help features of Python will make sure you can stop worrying about
your dwindling resources, and instead focus on writing more Python software.