Python Programming Introduction

Introduction

Python is an interpreted high level programming language. It is often classified as a "scripting language" and is considered similar to languages such as Perl, Tcl, or Ruby. The syntax of Python is loosely inspired by elements of C programming.

Python was created by Guido van Rossum around 1990 who named it in honor of Monty Python.

Skills Graph

Where to get Python?

Python.org is where you obtain Python. For the purposes of this course, you only need a basic installation. I recommend installing Python 3.6 or newer. Python 3.6 is used in the notes and solutions.

Why was Python created?

In the words of Python's creator:

My original motivation for creating Python was the perceived need for a higher level language in the Amoeba [Operating Systems] project. I realized that the development of system administration utilities in C was taking too long. Moreover, doing these things in the Bourne shell wouldn't work for a variety of reasons. ... So, there was a need for a language that would bridge the gap between C and the shell.

• Guido van Rossum

Where is Python on my Machine?

Although there are many environments in which you might run Python, Python is typically installed on your machine as a program that runs from the terminal or command shell. From the terminal, you should be able to type python like this:

$ python
Python 3.8.1 (default, Feb 20 2020, 09:29:22)
[Clang 10.0.0 (clang-1000.10.44.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> print("hello world")
hello world
>>>

If you are new to using the shell or a terminal, you should probably stop, finish a short tutorial on that first, and then return here.

Although there are many non-shell environments where you can code Python, you will be a stronger Python programmer if you are able to run, debug, and interact with Python at the terminal. This is Python's native environment. If you are able to use Python here, you will be able to use it everywhere else.

Exercise 1.1: Using Python as a Calculator

On your machine, start Python and use it as a calculator to solve the following problem.

Lucky Larry bought 75 shares of Google stock at a price of $235.14 per share. Today, shares of Google are priced at $711.25. Using Python's interactive mode as a calculator, figure out how much profit Larry would make if he sold all of his shares.

>>> (711.25 - 235.14) * 75
35708.25
>>>

Pro-tip: Use the underscore (_) variable to use the result of the last calculation. For example, how much profit does Larry make after his evil broker takes their 20% cut?

>>> _ * 0.80
28566.600000000002
>>>

Exercise 1.2: Getting help

Use the help() command to get help on the abs() function. Then use help() to get help on the round() function. Type help() just by itself with no value to enter the interactive help viewer.

One caution with help() is that it doesn't work for basic Python statements such as for, if, while, and so forth (i.e., if you type help(for) you'll get a syntax error). You can try putting the help topic in quotes such as help("for") instead. If that doesn't work, you'll have to turn to an internet search.

Followup: Go to http://docs.python.org and find the documentation for the abs() function (hint: it's found under the library reference related to built-in functions).

Exercise 1.3: Cutting and Pasting

This course is structured as a series of traditional web pages where you are encouraged to try interactive Python code samples by typing them out by hand. If you are learning Python for the first time, this "slow approach" is encouraged. You will get a better feel for the language by slowing down, typing things in, and thinking about what you are doing.

If you must "cut and paste" code samples, select code starting after the >>> prompt and going up to, but not any further than the first blank line or the next >>> prompt (whichever appears first). Select "copy" from the browser, go to the Python window, and select "paste" to copy it into the Python shell. To get the code to run, you may have to hit "Return" once after you've pasted it in.

Use cut-and-paste to execute the Python statements in this session:

>>> 12 + 20
32
>>> (3 + 4
         + 5 + 6)
18
>>> for i in range(5):
        print(i)

0
1
2
3
4
>>>

Warning: It is never possible to paste more than one Python command (statements that appear after >>>) to the basic Python shell at a time. You have to paste each command one at a time.

Now that you've done this, just remember that you will get more out of the class by typing in code slowly and thinking about it--not cut and pasting.

Summary

Congratulations! You have completed the Python Introduction lab. You can practice more labs in LabEx to improve your skills.