Friday, 2 September 2011

A Beginner's Python Reference

Scope:
Convention is to use four spaces (and no tabs) for each level of indentation

Console output: 
print "Hello, world!"

Command line arguments:
import sys

for arg in sys.argv:
    print arg

if len(sys.argv) != 5:
    print 'Usage: example.exe '
    sys.exit(1)

print "First argument: ", sys.argv[1]
print "Second argument: ", sys.argv[2]
print "Third argument: ", sys.argv[3]
print "Fourth argument: ", sys.argv[4]

String literals:
String literals can be enclosed in matching single quotes (') or double quotes (").

String variables:
How to check whether string str is empty?
if str


String concatenation:
name = 'Bojan'
print "Name:"+name
print "Name:",name
sys.stdout.write(name)
sys.stdout.write("\n")
name += '\n'
sys.stdout.write(name)
sys.stdout.write('\"' + name + '\"')
sys.stdout.write('\n')
Output:
Name:Bojan
Name: Bojan
Bojan
Bojan
"Bojan
"

Type conversions:
print "i = " + i fails: TypeError: cannot concatenate 'str' and 'int' objects. i needs to be converted to string first:
str(i)
- converts integer i into string

Logical operators:
not, and, or. (a and b) is evaluated only if a is True. (a or b) is evaluated only if a is False.

Function return values:
Functions can return a single or multiple values.

Return statement is return.

Example when function returns a pair:
   drive, tail = os.path.splitdrive(path)

How to terminate application and return error code:
sys.exit(4)

How to make application to wait for user to press Enter?
raw_input('Press Enter...')

Defining and using a class:
class CPerson:
    def __init__(self, name = ""):
        self.name = name
    def print_name(self):
        sys.stdout.write(self.name + "\n")
...
person = CPerson()
person.name = "Bojan"
person.print_name()

Enumerations
class EnumType:
       Value1 = 1
       Value2 = 2
       ...

x = EnumType.Value2
[source]

Links and references:
Python v2.7.2 documentation
Dive into Python

Python coding guidelines:
Style Guide for Python Code

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