Python Guide: From Zero to Hero Part 1

This is a detailed tutorial designed for coders who need to learn the Python programming language from scratch. In this course I will try to highlight many of Python's capabilities and features. Python is an easy-to-learn programming language.



Your First Program

>>> print "Hello World"
Hello World
>>>

On UNIX:

#!/usr/local/bin/python
print "Hello World"

Expressions

Expressions are the same as with other languages as in the following:

1 + 3
1 + (3*4)
1 ** 2
’Hello’ + ’World’

Variables

Variables are not tied to a memory location like in C. They are dynamically typed.

a = 4 << 3
b = a * 4.5

if-else

# find maximum (z) of a and b
if a < b:
z = b
else:
z = a

elif statement

PS: There is no “switch” statement.

if a == ’+’:
op = PLUS
elif a == ’-’:
op = MINUS
elif a == ’*’:
op = MULTIPLY
else:
op = UNKNOWN

The while statement

while a < b:
# Do something
a = a * 2

The for statement

for i in [3, 4, 10, 25]:
print i
Tuples:

Tuples are like lists, but the size is fixed at the time of creation.

f = (2,3,4,5) # A tuple of integers

Functions

# Return a+b
def Sum(a,b):
s = a+b
return s

# Now use it
a = Sum(2,5) # a = 7

Files

f = open("foo","w") # Open a file for writing
g = open("bar","r") # Open a file for reading
"r" Open for reading
"w" Open for writing (truncating to zero length)
"a" Open for append
"r+" Open for read/write (updates)
"w+" Open for read/write (with truncation to zero length)

Examples of string processing functions

string.atof(s) # Convert to float
string.atoi(s) # Convert to integer
string.atol(s) # Convert to long
string.count(s,pattern) # Count occurrences of pattern in s.