Print vs Return

Here are two different method declarations:

def f1(x):

print x + 1 def f2(x):

return x + 1

What happens when  we call them?

>>> f1(3)

4

>>> f2(3)

4

It looks like they behave in exactly the similar way.  But they don't, exactly.  Look at this example:

>>> print(f1(3))

4

None

>>> print(f2(3))

4

In the case of f1, the function, when  calculated, prints 4; then  it gives the value  None, which  is given by the Python file. In the case of f2, it does not give  anything, but it gives 4, which  is printed by the Python core. Finally, we may look the difference here:

>>> f1(3) + 1

4

Traceback (most recent call last):

File "", line 1, in ?

TypeError: unsupported operator type(s) for +: 'NoneType' and 'int'

>>> f2(3) + 1

5

In the ?rst case, the function does not give a value,  so there  is nothing to include  to 1, and an error is created. In the second  type, the function gives the value  4, which  is included to 1, and  the result,  5, is output by the Python read-eval-print loop.

Print  is very needful  for debugging. It is very important to know  that you may print  out as many  values as you want  in one line:

>>> x = 100

>>> print 'x', x, 'x squared', x*x, 'xiv', 14

x 100 x squared 10000 xiv 14

We have also snuck in another data type on you: strings. A string  is a sequence of words. You can build a string  using  single or double quotes;  and access individual elements of strings using indexing.

>>> s1 = 'hello world'

>>> s2 = "hello world"

>>> s1 == s2

True

>>> s1[3]

'l'

As you  may  see,  indexing indicates  to the  extraction of a particular element of a string,  by using square brackets [i] where i is a number that  identi?es the  location  of the  character that  you wish to extract (note that the indexing starts  with 0 ).