Python Programming Tutorial-Page1
What is Python?
An Interpreted high-level programming language similar to Perl, Ruby, Tcl, and other so-called scripting languages created by Guido Van Rossum around 1990 and named in the honor of Monty Python.
Common applications and non-uses of Python
• Text processing/data processing
• Application scripting
• Systems administration/programming
• Internet programming
• Graphical user interfaces
Python is not suitable for device drivers and low-level systems,computer graphics,
visualization, and games and for numerical algorithms/scientific computing.
But Python is still used in these application domains, but only as a high-level control language. Important computations are actually carried out in C, C++, Fortran, etc. For example, you would not implement matrix multiplication in Python.
• Python programs run inside an interpreter
• The interpreter is a simple console-based application that normally starts from a command shell (e.g. the Unix shell)
shell % python
Python 2.5.1 (r251:54869, Apr 18 2007, 22:08:04)
[GCC 4.0.1 (Apple Computer, Inc. build 5367)] on darwin
Type "help", "copyright", "credits" or "license"
• Expert programmers usually have no problem using the interpreter in this way , but it is not so user-friendly for beginners.
• Python includes a simple integrated development called IDLE (which is another Monty Python reference)
The Python Interpreter
• When you start Python, you get an "interactive" mode where you can experiment
• If you start typing statements, they will run immediately
• No edit/compile/run/debug cycle
• In fact, there is no "compiler"
The interpreter runs a "read-eval" loop
>>> print "hello world"
>>> for i in range(5):
... print i
Type help() with no name for interactive help
Documentation is available at http://docs.python.org
Creating python program
• Programs are put in .py files
• Source files are simple text files
• Create with your favorite editor (e.g. emacs)
• Can also edit programs with IDLE or other Python IDE
• A Python program is a sequence of statements
• Each statement is terminated by a newline
• Statements are executed one after the other until you reach the end of the file.
• When there are no more statements, the program stops
Comments are denoted by #
# This is a comment
height = 442 # Meters
Extend to the end of the line
There are no block comments in Python (e.g., /* ... */)
A variable is just a name for some value
Variable names follow same rules as C
You do not declare types (int, float, etc.)
height = 442 # An integer
height = 442.0 # Floating point
height = "Really tall" # A string
Differs from C++/Java where variables have a fixed type that must be declared.
Variables can not have one of these names
These are mostly C-like and have the same meaning in most cases
• Python is case sensitive
• These are all different variables:
name = "Jake"
• Language statements are always lower-case
print "Hello World" # OK
PRINT "Hello World" # ERROR
while x < 0: # OK
WHILE x < 0: # ERROR
The while statement executes a loop
while thickness <= height:
thickness = thickness * 2
numfolds = numfolds + 1
print numfolds, thickness
Indentation used to denote blocks of code Indentation must be consistent Colon (:) always indicates start of new block while thickness <= height: There is a preferred indentation style Always use spaces Use 4 spaces per level Avoid tabs Always use a Python-aware editor
if a < b:
print "Computer says no"
print "Computer says yes"
if a == '+':
op = PLUS
elif a == '-':
op = MINUS
elif a == '*':
op = TIMES
op = UNKNOWN
< > <= >= == !=
Boolean expressions (and, or, not)
if b >= a and b <= c:
print "b is between a and c"
if not (b < a or b > c):
print "b is still between a and c"
Non-zero numbers, non-empty objects also evaluates as True
x = 42
# x ix non zero
The print statement
print "Your name is", name
print x, #Omits newline
Produces a single line of text