Conditionals- booleans, Python Programming

 

Booleans

 

Before we talk about  conditionals, we require  to clarify the Boolean  data  type.  It has two values False and True. Typical statement that have Boolean values  are numerical comparisons:

 

>>> 7 > 8

False

>>> -6 <= 9

True

 

We can also test  whether data  items  are equal  to each other.  Usually we use  == to test  for equality. It gives True if the two  objects have  same  values.   Sometimes, however, we will be study in knowing whether the two items are the exact same object. In that case we use is:

 

>>> [1, 2] == [1, 2]

True

>>> [1, 2] is [1, 2]

False

>>> a = [1, 2]

>>> b = [1, 2]

>>> c = a

>>> a == b

True

>>> a is b

False

>>> a == c

True

>>> a is c

True

 

Thus, in the examples above, we see that == testing  can be applied to nested loops, and basically gives true  if every one of the individual elements is the similar.  However, is testing,  especially when  applied to nested loops, is more defined, and only returns True if the two objects point to exactly the same instance in memory.

In addition, we can combine Boolean values  conveniently using  and, not, and or:

 

>>> 7 > 8 or 8 > 7

True

>>> not 7 > 8

True

>>> 7 == 7 and 8 > 7

True

 

If

 

Basic conditional instructions have the form:5

if :

else:

 

 

When  the  interpreter encounters a  conditional statement, it  starts  by  evaluating  ,   getting either   True or  False as  a  result.6   If  the given result   is  True,  then   it  will  eval­ uate  ,...,;  if it is not true,  then  it will evaluate ,...,. Crucially, it always calculates only one set of the statements.

 

Now, for example, we can create a functionthat returns the absolute value of its argument.

 

def abs(x):

if x >= 0:

return x

else:

return -x

 

 

We could also have written

def abs(x):

if x >= 0:

result = x

else:

result = -x

return result

 

Python uses the level of indentation of the instructions to decide  which  ones go in the groups of statements governed by the conditionals; so, in the example above, the return result statement is evaluated once the conditional is done,  no matter which  branch  of the conditional is evaluated.

 

Posted Date: 8/9/2012 7:02:10 AM | Location : United States







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