Python
Programming Notes and Practical Programs BCA 3rd Semester CSJM
University Kanpur
Python Keywords and Identifiers with examples
What is a Python Keyword?
A python keyword is a reserved word which you can’t use as a name of your variable, class, function etc.
These keywords have a special meaning and they are
used for special purposes in Python programming language.
For example – Python keyword “while” is used for
while loop thus you can’t name a variable with the name “while” else it may
cause compilation error.
There are total 33 keywords in Python 3.6.
Example of Python keyword
In the following example we are using while keyword
to create a loop for displaying the values of variables num as long as they are
greater than 5.
num = 10
while num>5:
print(num)
num -= 1
Output:
10
9
8
7
6
Python Identifiers
In the last article, we discussed about variables
in Python.
Variable name is known as identifier. There are few
rules that you have to follow while naming the variables in Python.
For example here the variable is of integer type that
holds the value 10. The name of the variable, which is num is called
identifier.
num = 10
1. The name of the variable must always start with
either a letter or an underscore (_). For example: _str, str, num, _num are all
valid name for the variables.
2. The name of the variable cannot start with a number. For example: 9num is
not a valid variable name.
3. The name of the variable cannot have special characters such as %, $, # etc,
they can only have alphanumeric characters and underscore (A to Z, a to z, 0-9
or _).
4. Variable name is case sensitive in Python which means num and NUM are two
different variables in python.
Python identifier example
In the following example we have three variables.
The name of the variables num, _x and a_b are the
identifiers.
# few examples of identifiers
num = 10
print(num)
_x = 100
print(_x)
a_b = 99
print(a_b)
Output:
10
100
99
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