Introduction to Python

Creating your own functions

A method (function) can be created with "def" command as follows:

def greeting(): print "How are you doing?" greeting()

$ How are you doing?

You can make a method that takes an argument:

def hello(name): print "Hello %s" %name hello("Jack.")

$ Hello Jack.

A method that takes more than one argument can be done as follows:

def hi(name,num): print "Hi %s " %name *num hi("Steve!",3)

$ Hi Steve! Hi Steve! Hi Steve!

After defining a function, you can operate it on a list.

def square(x): return x*x print map(square, [1,2,5])

$ [1, 4, 25]

Instead of using the defined function, you can use 'lambda' as a nameless function. The above code can be rewritten as follows:

print map(lambda x: x*x, [1,2,5])

Let's define the following function:

def sign(n): if n>=0: return 1 # 1 is true. else: return 0:

An "if" statement also returns a boolean value.

y=input("Enter a value.") if sign(y): print y, " is a positive value." else: print y, " is a negative value."

$ Enter a value. 8 $ 8 is a positive value.

The following code is to count words. The file, "test.py", can be any text file in the same directory.

import string def couwords(m): list = string.split(m) return len(list) inp = open("test.py","r") tot = 0 for line in inp.readlines(): tot=tot+couwords(line) print "This file has %s word(s)." %tot inp.close()

$ This file has 8 word(s).

Python has recursive call. By using it, you can create a function that calculates factorial without a for loop.

def facto(k): if(k==0)or(k==1): return 1 else: return k*facto(k-1) j = input('Type a positive integer.') result=facto(j) print result