Python Quick Guide
Python Overview:
Python is a high-level, interpreted, interactive and object oriented-scripting language.
Python is Interpreted
Python is Interactive
Python is Object-Oriented
Python is Beginner's Language
Python was developed by Guido van Rossum in the late eighties and early nineties at the National Research Institute for Mathematics and Computer Science in the Netherlands.
Python's feature highlights include:
Easy-to-learn
Easy-to-read
Easy-to-maintain
A broad standard library
Interactive Mode
Portable
Extendable
Databases
GUI Programming
Scalable
Getting Python:
The most up-to-date and current source code, binaries, documentation, news, etc. is available at the official website of Python:
Python Official Website :http://www.python.org/
You can download the Python documentation from the following site. The documentation is available in HTML, PDF, and PostScript formats.
Python Documentation Website :www.python.org/doc/
First Python Program:
Interactive Mode Programming:
Invoking the interpreter without passing a script file as a parameter brings up the following prompt:
root# python
Python 2.5 (r25:51908, Nov 6 2007, 16:54:01)
[GCC 4.1.2 20070925 (Red Hat 4.1.2-27)] on linux2
Type "help", "copyright", "credits" or "license" for more info.
>>>
Type the following text to the right of the Python prompt and press the Enter key:
>>> print "Hello, Python!";
This will produce following result:
Hello, Python!
Python Identifiers:
A Python identifier is a name used to identify a variable, function, class, module, or other object. An identifier starts with a letter A to Z or a to z or an underscore (_) followed by zero or more letters, underscores, and digits (0 to 9).
Python does not allow punctuation characters such as @, $, and % within identifiers. Python is a case sensitive programming language. ThusManpower and manpower are two different identifiers in Python.
Here are following identifier naming convention for Python:
Class names start with an uppercase letter and all other identifiers with a lowercase letter.
Starting an identifier with a single leading underscore indicates by convention that the identifier is meant to be private.
Starting an identifier with two leading underscores indicates a strongly private identifier.
If the identifier also ends with two trailing underscores, the identifier is a language-defined special name.
Reserved Words:
The following list shows the reserved words in Python. These reserved words may not be used as constant or variable or any other identifier names.
and
exec
not
assert
finally
or
break
for
pass
class
from
continue
global
raise
def
if
return
del
import
try
elif
in
while
else
is
with
except
lambda
yield
Lines and Indentation:
One of the first caveats programmers encounter when learning Python is the fact that there are no braces to indicate blocks of code for class and function definitions or flow control. Blocks of code are denoted by line indentation, which is rigidly enforced.
The number of spaces in the indentation is variable, but all statements within the block must be indented the same amount. Both blocks in this example are fine:
if True:
print "True"
else:
print "False"
However, the second block in this example will generate an error:
if True:
print "Answer"
print "True"
else:
print "Answer"
print "False"
Multi-Line Statements:
Statements in Python typically end with a new line. Python does, however, allow the use of the line continuation character (\) to denote that the line should continue. For example:
total = item_one + \
item_two + \
item_three
Statements contained within the [], {}, or () brackets do not need to use the line continuation character. For example:
days = ['Monday', 'Tuesday', 'Wednesday',
'Thursday', 'Friday']
Quotation in Python:
Python accepts single ('), double (") and triple (''' or """) quotes to denote string literals, as long as the same type of quote starts and ends the string.
The triple quotes can be used to span the string across multiple lines. For example, all the following are legal:
word = 'word'
sentence = "This is a sentence."
paragraph = """This is a paragraph. It is
made up of multiple lines and sentences."""
Comments in Python:
A hash sign (#) that is not inside a string literal begins a comment. All characters after the # and up to the physical line end are part of the comment, and the Python interpreter ignores them.
#!/usr/bin/python
# First comment
print "Hello, Python!"; # second comment
This will produce following result:
Hello, Python!
A comment may be on the same line after a statement or expression:
name = "Madisetti" # This is again comment
You can comment multiple lines as follows:
# This is a comment.
# This is a comment, too.
# This is a comment, too.
# I said that already.
Using Blank Lines:
A line containing only whitespace, possibly with a comment, is known as a blank line, and Python totally ignores it.
In an interactive interpreter session, you must enter an empty physical line to terminate a multiline statement.
Multiple Statements on a Single Line:
The semicolon ( ; ) allows multiple statements on the single line given that neither statement starts a new code block. Here is a sample snip using the semicolon:
import sys; x = 'foo';sys.stdout.write(x + '\n')
Multiple Statement Groups as Suites:
Groups of individual statements making up a single code block are called suites in Python.
Compound or complex statements, such as if, while, def, and class, are those which require a header line and a suite.
Header lines begin the statement (with the keyword) and terminate with a colon ( : ) and are followed by one or more lines which make up the suite.
Example:
if expression :
suite
elif expression :
suite
else :
suite
Python - Variable Types:
Variables are nothing but reserved memory locations to store values. This means that when you create a variable you reserve some space in memory.
Based on the data type of a variable, the interpreter allocates memory and decides what can be stored in the reserved memory. Therefore, by assigning different data types to variables, you can store integers, decimals, or characters in these variables.
Assigning Values to Variables:
The operand to the left of the = operator is the name of the variable, and the operand to the right of the = operator is the value stored in the variable. For example:
counter = 100 # An integer assignment
miles = 1000.0 # A floating point
name = "John" # A string
print counter
print miles
print name
Standard Data Types:
Python has five standard data types:
Numbers
String
List
Tuple
Dictionary
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