Engineering Tutorials
Introduction to Python language
In this tutorial we will learn how to program in the python language.
What is python
Python is a high level script language, it's produces a very clean and organized code because it uses identation as block delimiters, it also support object oriented paradigm. Bellow is a code sample:
Python Standard library
Python's standard library is very complete, it has modules for database handling, standard internet protocols, graphical user interface, etc...
Installation
Download Python-2.4.1.exe , after that install it, and test at the DOS by typing "python -V"
Now go to and run the "python shell", after you get the ">>>" type print "hello world!"
You can also try 1+2, 2*2, 3**2 (Exponential)
print "1+2=", 1+2 (Simple sum)
Here is a list of common arithmetic operators:
| command | name | example | output |
|---|---|---|---|
| + | Addition | 4+5 | 9 |
| - | Subtraction | 2-2 | 0 |
| * | Multiplication | 3*3 | 9 |
| / | Division | 7/2 | 3 |
| % | Reminder | 7%2 | 1 |
| ** | Expoent | 8**2 | 64 |
Comments
Comments are used to help you remember what that old routine does :) (Even so there is times that I just can't remember). Comments are ignored by the python interpreter.
# This is a comment
Variables
Python don't need variable declaration, just type a name and assign a value, that python will create a variable, python is not strongly-typed language so some care must be taken in order to avoid some commom bugs.
Creating a program
Python programs are just text files (.py) that will be passed to python. In the video bellow we show how to create a simple program with variables and comments.
Strings
Strings are a sequence of alphanumerical value, a string variable can be declared like this.
>>> var_string = "SomeString"
A variable called var_string will store the value "SomeString"
Loops statements
In python and in most languages we have these loop statements
- for
- while
Those statements are used when you have to repeat a group of instructions many times based in some condition.
Before the for, and while statements let's first see the boolean operators
| operator | function |
|---|---|
| < | less |
| <= | less or equal |
| > | greater |
| >= | greater or equal |
| != | not equal |
| <> | not equal |
| == | equal |
while
The while statement will execute a block of instructions while some condition is true. For example
while condition:
instructions1
instructions2
instructionsn...
Observe that the block of instructions of the while statement has a identation.
for
The for statement in Python differs a bit from what you may be used to in C or Pascal. Rather than always iterating over an arithmetic progression of numbers Python’s for statement iterates over the items of any sequence (a list or a string), in the order that they appear in the sequence. For example:
Condition statement
Conditions create a area of code that will be executed only if a condition is met. In python we have these condition statements
- if
if syntax
The if statement means that something will be executed if some condition is met:
if condition:
doSomething;
elseif otherCondition:
doSomething;
else:
doDefaultSomething;
Example:
Functions
In python and in most programming languages, functions are block of codes that can accept arguments and return a value.
def functionname(arg1, arg2, ...):
statement1;
statement2;
statementn...;
return someValue;
x = functionname(1,2,...);
One can also define a function with no arguments and no return value.
