Computer Programming I

A Quick Tutorial for Python Syntax

July 8, 2013

For some, Python is far from their first language. For others, it is where they had started programming. I have received several comments and emails from readers asking how to proceed after understanding the basic concepts in Python. I am hoping to put together a road-map into Python in the next few weeks. Whether you know Python already or want to learn the basic quickly, I hope you will find this post (and the rest) useful. This is a very quick paste, high overview of the language. You are expected to know the basics of programming. Think of this as fast Python syntax review. For this tutorial I will use Python2.7. I highly recommend you consult the Python2.7 documentation while coding or download Python2.7 documentation for offline use. Linux and Mac come with Python already pre-installed. If you require help setting up a Python environment, please consult the Python installation guide. I am going to assume from this point on you already have Python 2.7 at least installed on your system. So let us get to it:

Running Python

There are 3 ways to execute Python code:

  1. The Python Interpreter - an interactive terminal. Statements are evaluated as entered.
  2. Loading a file into the Python Interpreter - save any text file as a .py and execute the statements.
  3. Compiled Python - this is not for speed of execution, rather for sharing a program without sharing code.

For any of the ways, we are going to focus on command line only. There are IDEs for Python, however they are an overkill for this tutorial. To run Python, simply lunch your terminal and type ‘python’. If you want to run a .py file in the terminal type ‘python <file_name.py>’, where file_name should be replaced with your file name.

Comments

In Python, any line starting with the ‘#’ symbol is considered a comment and will be ignored by the Interpreter.

Python Basic Data Types

Similar to other languages, Python supports the idea of basic data types. Unlike most low-level languages, Python does not require the programmer to specify the type. Python interrupter takes case of the data type for you. You may also change to type throughout the program. Thankfully, Python has a built in function type() that can clarify what type of data Python ‘thinks’ the variable is. The basic data types are:

* integer
* long
* float
* complex
* string
* boolean

Here is an output from the Python interpreter:

wpid-pythonbasicdatatypes-2013-01-20-10-09.png

Python Data Structures

Python has 4 data structures that could be at your disposal. These are complex data types that are built from the basic data types we saw before. Each of the data structure types has different usage and attributes. We will discuss:

* Lists
* Tuples
* Dictionaries
* Sets

Starting from the top, Lists are the most common data structure used in Python. With Lists you can group basic datatypes or even data structures together. You can preform numbers standard library function on lists. The 2 (2things) most important things to remember about lists are:

* They are 0 and reversed numeric indexed
* They are mutable

Let us look at some list example operations:

wpid-pythonlists2-2013-01-20-10-09.png

Moving on to tuples, they are very similar to lists but with one thing apart. Tuples are immutable. You may think of tuples as immutable lists, in other words lists that can not be changed once you create them. All the operations we have done on lists apply to Tuples, however, we cannot remove or add elements. This means that when we initiate a Tuple we initiate it with values that may never change. Let us look at some simple Tuple operations:

wpid-pythontupleexamples2-2013-01-20-10-09.png

So now that we have some data types we can move on to the next vital piece of information you need to know, Python Standard Library. Python include a huge array of functions you can use without anything special. The type() and len() functions are some examples of the functions that are included in standard library. This also includes function such as input() and raw_input(), string and number manipulation and many more functions. The best advice if you are looking for a function, check if it is included in stadard library before going to far.

So now what do we do if a function is not in standard library. For example, lets say we need to comute a sin() of an angle, or require the value of pi for calculation, what do we do then? Well, in that case we can import a library. That is right, in addtion to the huge standard library there is also a "secondary library" with everything you might think about, at least in the beginning. Again, you can refer to the Python2.7 documentation for any reference to these libraries. In our case we can import the math library and directly call the math.sin() function or access the value of math.pi. Let us take a look:

 

python_math_import_example3

 

Python is truly a fun language to begin to code with. I did not begin with Python myself, but I highly recommend it to others. Why? well, first I do not think anyone should start in PASCAL any more. Although it was a good educational languages, it is pointless to learn today. Second, Python is natural. It is easy to ease in to programming with python far more than any other language. (This last point might be debatable on the person and the teacher).

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