Every language contains words and a set of rules that would make a sentence meaningful. Similarly, in Python programming language, there are a set of predefined words, called Keywords which along with Identifiers will form meaningful sentences when used together. Python keywords cannot be used as the names of variables, functions, and classes.
In this article, we will learn about Python keywords and how to use them to perform some tasks.
Python Keywords
Keywords in Python are reserved words that can not be used as a variable name, function name, or any other identifier.
List of Keywords in Python
| and |
It is a Logical Operator
|
False |
Represents an expression that will result in not being true.
|
nonlocal |
It is a non-local variable
|
| as |
It is used to create an alias name
|
finally |
It is used with exceptions
|
not |
It is a Logical Operator
|
| assert |
It is used for debugging
|
for |
It is used to create Loop
|
or |
It is a Logical Operator
|
| break |
Break out a Loop
|
from |
To import specific parts of a module
|
pass |
pass is used when the user doesn’t
want any code to execute
|
| class |
It is used to define a class
|
global |
It is used to declare a global variable
|
raise |
raise is used to raise exceptions or errors.
|
| continue |
Skip the next iteration of a loop
|
if |
To create a Conditional Statement
|
return |
return is used to end the execution
|
| def |
It is used to define the Function
|
import |
It is used to import a module
|
True |
Represents an expression that will result in true.
|
| del |
It is used to delete an object
|
is |
It is used to test if two variables are equal
|
try |
Try is used to handle errors
|
| elif |
Conditional statements, same as else-if
|
in |
To check if a value is present in a Tuple, List, etc.
|
while |
While Loop is used to execute a block of statements
|
| else |
It is used in a conditional statement
|
lambda |
Used to create an anonymous function
|
with |
with statement is used in exception handling
|
| except |
try-except is used to handle these errors
|
None |
It represents a null value
|
yield |
yield keyword is used to create a generator function
|
Getting the List of all Python keywords
We can also get all the keyword names using the below code.
Python3
import keyword
print("The list of keywords is : ")
print(keyword.kwlist)
|
Output:
The list of keywords are:
['False', 'None', 'True', 'and', 'as', 'assert', 'async', 'await', 'break',
'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if',
'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']
Let’s discuss each keyword in detail with the help of good examples.
True, False, None Keyword in Python
- True: This keyword is used to represent a boolean true. If a statement is true, “True” is printed.
- False: This keyword is used to represent a boolean false. If a statement is false, “False” is printed.
- None: This is a special constant used to denote a null value or a void. It’s important to remember, 0, any empty container(e.g. empty list) does not compute to None.
It is an object of its datatype – NoneType. It is not possible to create multiple None objects and can assign them to variables.
True, False, and None Use in Python
False is 0, and True is 1.True + True + True is 3.True + False + False is 1.None isn’t equal to 0 or an empty list ([]).
Python3
print(False == 0)
print(True == 1)
print(True + True + True)
print(True + False + False)
print(None == 0)
print(None == [])
|
Output
True
True
3
1
False
False
and, or, not, in, is In Python
Python and Keyword
This a logical operator in Python. “and” Return the first false value. If not found return last. The truth table for “and” is depicted below.
3 and 0 return 0
3 and 10 return 10
10 or 20 or 30 or 10 or 70 returns 10
The above statements might be a bit confusing to a programmer coming from a language like C where the logical operators always return boolean values(0 or 1). The following lines are straight from the Python docs explaining this:
The expression x and y first evaluates x; if x is false, its value is returned; otherwise, y is evaluated and the resulting value is returned.
The expression x or y first evaluates x; if x is true, its value is returned; otherwise, y is evaluated and the resulting value is returned.
Note that neither and nor restrict the value and type they return to False and True, but rather return the last evaluated argument. This is sometimes useful, e.g., if s is a string that should be replaced by a default value if it is empty, the expression s or ‘foo’ yields the desired value. Because not has to create a new value, it returns a boolean value regardless of the type of its argument (for example, not ‘foo’ produces False rather than ”.)
Python or Keyword
This a logical operator in Python. “or” Return the first True value. if not found return last. The truth table for “or” is depicted below.
3 or 0 returns 3
3 or 10 returns 3
0 or 0 or 3 or 10 or 0 returns 3
- not: This logical operator inverts the truth value. The truth table for “not” is depicted below.
- in: This keyword is used to check if a container contains a value. This keyword is also used to loop through the container.
- is: This keyword is used to test object identity, i.e to check if both the objects take the same memory location or not.
and, or, not, is and in keyword implementation in Python
The provided code demonstrates various Python operations:
- Logical Operations:
'or' returns ‘True' when at least one operand is ‘True'.'and' returns ‘True' only when both operands are ‘True'.'not' negates the operand.
- Python “in” Keyword:
- It checks if ‘s’ is in the string ‘geeksforgeeks’ and prints accordingly.
- It loops through the string’s characters.
- Python “is” Keyword:
- It checks if two empty strings (‘ ‘) are identical (returns ‘
True').
- It checks if two empty dictionaries ({}) are identical (returns ‘
False').
Python3
print(True or False)
print(False and True)
print(not True)
if 's' in 'geeksforgeeks':
print("s is part of geeksforgeeks")
else:
print("s is not part of geeksforgeeks")
for i in 'geeksforgeeks':
print(i, end=" ")
print("\r")
print(' ' is ' ')
print({} is {})
|
Output
True
False
False
s is part of geeksforgeeks
g e e k s f o r g e e k s
True
False
Iteration Keywords – for, while, break, continue in Python
- for: This keyword is used to control flow and for looping.
- while: Has a similar working like “for”, used to control flow and for looping.
- break: “break” is used to control the flow of the loop. The statement is used to break out of the loop and passes the control to the statement following immediately after loop.
- continue: “continue” is also used to control the flow of code. The keyword skips the current iteration of the loop but does not end the loop.
For, while, break, continue keyword Use in Python
The code includes a for loop and a while loop:
- For Loop: Iterates from 0 to 9, printing numbers. It breaks when 6 is encountered.
- While Loop: Initializes
i to 0 and prints numbers from 0 to 9. It skips printing when i is 6 and continues to the next iteration.
Python3
for i in range(10):
print(i, end=" ")
if i == 6:
break
print()
i = 0
while i < 10:
if i == 6:
i += 1
continue
else:
print(i, end=" ")
i += 1
|
Output
0 1 2 3 4 5 6
0 1 2 3 4 5 7 8 9
Conditional keywords in Python- if, else, elif
- if : It is a control statement for decision making. Truth expression forces control to go in “if” statement block.
- else : It is a control statement for decision making. False expression forces control to go in “else” statement block.
- elif : It is a control statement for decision making. It is short for “else if“
if, else, and elif keyword use in Python
The code checks the value of the variable i:
- If ‘
i' is 10, it prints “i is 10”.
- If ‘
i' is 20, it prints “i is 20”.
- If ‘
i' is neither 10 nor 20, it prints “i is not present.” In this case, it will print “i is 20” because the value of i is 20.
Python3
i = 20
if (i == 10):
print("i is 10")
elif (i == 20):
print("i is 20")
else:
print("i is not present")
|
Note: For more information, refer to out Python if else Tutorial.
Structure Keywords in Python : def, class, with, as, pass, lambda
Python def
def keyword is used to declare user defined functions.
def keyword in Python
The code defines a function named fun using the def keyword. When the function is called using fun(), it prints “Inside Function.” This code demonstrates the use of the def keyword to define and call a function in Python.
Python3
def fun():
print("Inside Function")
fun()
|
class in Python
class keyword is used to declare user defined classes.
Class Keyword in Python
This code defines a Python class named Dog with two class attributes, attr1 and attr2, and a method fun that prints these attributes. It creates an object Rodger from the Dog class, accesses the class attributes, and calls the method. When executed, it prints the values of attr1 and `attr2, and the method displays these values, resulting in the output shown.
Python3
class Dog:
attr1 = "mammal"
attr2 = "dog"
def fun(self):
print("I'm a", self.attr1)
print("I'm a", self.attr2)
Rodger = Dog()
print(Rodger.attr1)
Rodger.fun()
|
Output
mammal
I'm a mammal
I'm a dog
Note: For more information, refer to our Python Classes and Objects Tutorial .
With in Python
with keyword is used to wrap the execution of block of code within methods defined by context manager. This keyword is not used much in day to day programming.
With Keyword in Python
This code demonstrates how to use the with statement to open a file named 'file_path' in write mode ('w'). It writes the text 'hello world !' to the file and automatically handles the opening and closing of the file. The with statement is used for better resource management and ensures that the file is properly closed after the block is executed.
Python3
with open('file_path', 'w') as file:
file.write('hello world !')
|
as in Python
as keyword is used to create the alias for the module imported. i.e giving a new name to the imported module. E.g import math as mymath.
as Keyword In Python
This code uses the Python math module, which has been imported with the alias gfg. It calculates and prints the factorial of 5. The math.factorial() function is used to calculate the factorial of a number, and in this case, it calculates the factorial of 5, which is 120.
Python3
import math as gfg
print(gfg.factorial(5))
|
pass in Python
pass is the null statement in python. Nothing happens when this is encountered. This is used to prevent indentation errors and used as a placeholder.
Pass Keyword in Python
The code contains a for loop that iterates 10 times with a placeholder statement ‘pass', indicating no specific action is taken within the loop.
Python3
n = 10
for i in range(n):
pass
|
Lambda in Python
Lambda keyword is used to make inline returning functions with no statements allowed internally.
Lambda Keyword in Python
The code defines a lambda function g that takes an argument x and returns x cubed. It then calls this lambda function with the argument 7 and prints the result. In this case, it calculates and prints the cube of 7, which is 343.
Python3
g = lambda x: x*x*x
print(g(7))
|
Return Keywords in Python- Return, Yield
- return : This keyword is used to return from the function.
- yield : This keyword is used like return statement but is used to return a generator.
Return and Yield Keyword use in Python
The ‘return' keyword is used to return a final result from a function, and it exits the function immediately. In contrast, the ‘yield' keyword is used to create a generator, and it allows the function to yield multiple values without exiting. When ‘return' is used, it returns a single value and ends the function, while ‘yield' returns multiple values one at a time and keeps the function’s state.
Python3
def fun():
S = 0
for i in range(10):
S += i
return S
print(fun())
def fun():
S = 0
for i in range(10):
S += i
yield S
for i in fun():
print(i)
|
Output
45
0
1
3
6
10
15
21
28
36
45
Import, From in Python
import : This statement is used to include a particular module into current program.
from : Generally used with import, from is used to import particular functionality from the module imported.
Import, From Keyword use in Python
The ‘import' keyword is used to import modules or specific functions/classes from modules, making them accessible in your code. The ‘from' keyword is used with ‘import' to specify which specific functions or classes you want to import from a module. In your example, both approaches import the ‘factorial' function from the ‘math' module, allowing you to use it directly in your code.
Python3
from math import factorial
import math
print(math.factorial(10))
print(factorial(10))
|
Exception Handling Keywords in Python – try, except, raise, finally, and assert
- try : This keyword is used for exception handling, used to catch the errors in the code using the keyword except. Code in “try” block is checked, if there is any type of error, except block is executed.
- except : As explained above, this works together with “try” to catch exceptions.
- finally : No matter what is result of the “try” block, block termed “finally” is always executed.
- raise: We can raise an exception explicitly with the raise keyword
- assert: This function is used for debugging purposes. Usually used to check the correctness of code. If a statement is evaluated to be true, nothing happens, but when it is false, “AssertionError” is raised. One can also print a message with the error, separated by a comma.
try, except, raise, finally, and assert Keywords use in Python
Example 1: The provided code demonstrates the use of several keywords in Python:
try and except: Used to handle exceptions, particularly the ZeroDivisionError, and print an error message if it occurs.finally: This block is always executed, and it prints “This is always executed” regardless of whether an exception occurs.assert: Checks a condition, and if it’s False, raises an AssertionError with the message “Divide by 0 error.”raise: Raises a custom exception (TypeError) with a specified error message if a condition is not met.
Python3
a = 4
b = 0
try:
k = a//b
print(k)
except ZeroDivisionError:
print("Can't divide by zero")
finally:
print('This is always executed')
print("The value of a / b is : ")
assert b != 0, "Divide by 0 error"
print(a / b)
temp = "geeks for geeks"
if temp != "geeks":
raise TypeError("Both the strings are different.")
|
Output
Can't divide by zero
This is always executed
The value of a / b is :
AssertionError: Divide by 0 error
Example 2: This code uses the raise keyword to raise a custom TypeError exception if two strings are not equal.
Python3
temp = "geeks for geeks"
if temp != "geeks":
raise TypeError("Both the strings are different.")
|
Output
TypeError: Both the strings are different.
Note: For more information refer to our tutorial Exception Handling Tutorial in Python.
del in Python
del is used to delete a reference to an object. Any variable or list value can be deleted using del.
del Keyword in Python
In this code, the variables my_variable1 and my_variable2 are initially defined and then deleted using the del keyword. When you try to print them after deletion, you will encounter a NameError because the variables no longer exist.
Python3
my_variable1 = 20
my_variable2 = "GeeksForGeeks"
print(my_variable1)
print(my_variable2)
del my_variable1
del my_variable2
print(my_variable1)
print(my_variable2)
|
Output
20
GeeksForGeeks
NameError: name 'my_variable1' is not defined
Global, Nonlocal in Python
global: This keyword is used to define a variable inside the function to be of a global scope.
non-local : This keyword works similar to the global, but rather than global, this keyword declares a variable to point to variable of outside enclosing function, in case of nested functions.
Global and nonlocal keywords in Python
In this code, the ‘global' keyword is used to declare global variables ‘a' and ‘b'. Then, there’s a function ‘add' that adds these global variables and prints the result.
The second part of the code demonstrates the ‘nonlocal' keyword. The function fun contains a variable var1, and within the nested function gun, we use nonlocal to indicate that we want to modify the var1 defined in the outer function fun. It increments the value of var1 and prints it.
Python3
a = 15
b = 10
def add():
c = a + b
print(c)
add()
def fun():
var1 = 10
def gun():
nonlocal var1
var1 = var1 + 10
print(var1)
gun()
fun()
|
Note: For more information, refer to our Global and local variables tutorial in Python.
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