Data Handling

Truth Values

Truth values are basically logical values of some data.

It can have either of two values : True / False

In python, except : False, "", '', '''''', """""", None, 0, {}, [] and () have a truth value as False.

Truth Value of some data can be found out using bool(x), where x is some data.

Lets test it out :

>>> bool("Hello")
True
>>> bool(0)
False
>>> bool(None)
False
>>> bool(1)
True
>>> bool(3.56)
True
>>> bool([1,50,97])
True
>>> bool({})
False

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Logical Operators

As discussed earlier the logical operators in python are : and, or, not.

not Operator

is the inverse operator it will invert every result (True becomes False and False Becomes True).

>>> not True
False
>>> not False
True

or Operator

Is an operator which returns True if either of the conditions specified is True. If both conditions specified are False then it returns False.

>>> 5 > 3 or 2 < 1
True
>>> 10 > 20 or 11 > 200
False
>>> 1 < 2 or 2 < 3 #it will return True even if both conditions specified are True
True

and operator

Returns True only if both conditions are True otherwise it will return False.

>>> 5 > 3 and 2 < 1
False
>>> 200 < 1 and 2 > 1
False
>>> 1 == 1 and 500 != 21
True
>>> 23 < 25 and 5 > 1
True

Some Errors which do not show up

These errors would show up when used individually but they are not read by python because :

(i) the or operator only reads the second condition if the first condition is True

3 > 2 or a > b #a and b are not defined yet we are comparing them
True
>>> #no errors

(ii) the and operator only reads the second condition if the second condition is False

>>> 3 < 2 and a != b
False
>>> #no errors yet again

Lets confirm that they do give errors if used individually:

>>> a > b
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'a' is not defined
>>> a != b
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'a' is not defined