Check whether given Key already exists in a Python Dictionary

Given a dictionary in Python, write a Python program to check whether a given key already exists in a dictionary. If present, print “Present” and the value of the key. Otherwise print “Not present”.

Examples:

Input : {'a': 100, 'b':200, 'c':300}, key = b
Output : Present, value = 200

Input : {'x': 25, 'y':18, 'z':45}, key = w
Output : Not present

Approach #1 : Using Inbuilt method keys()

keys() method returns a list of all the available keys in the dictionary. With the Inbuilt method keys(), use if statement and the ‘in’ operator to check if the key is present in the dictionary or not.

# Python3 Program to check whether a
# given key already exists in a dictionary.

# Function to print sum
def checkKey(dict, key):

    if key in dict.keys():
        print("Present, ", end =" ")
        print("value =", dict[key])
    else:
        print("Not present")

# Driver Code
dict = {'a': 100, 'b':200, 'c':300}

key = 'b'
checkKey(dict, key)

key = 'w'
checkKey(dict, key)

Output:

Present, value = 200
Not present

Approach #2 : Using if and in

This method simply uses if statement to check whether the given key exist in the dictionary.

# Python3 Program to check whether a
# given key already exists in a dictionary.

# Function to print sum
def checkKey(dict, key):

    if key in dict:
        print("Present, ", end =" ")
        print("value =", dict[key])
    else:
        print("Not present")

# Driver Code
dict = {'a': 100, 'b':200, 'c':300}

key = 'b'
checkKey(dict, key)

key = 'w'
checkKey(dict, key)

Output:

Present, value = 200
Not present

Approach #3 : Using Inbuilt method has_key()

has_key() method returns true if a given key is available in the dictionary, otherwise it returns a false. With the Inbuilt method has_key(), use if statement to check if the key is present in the dictionary or not.

Note – has_keys() method has been removed from Python3 version. Therefore, it can be used in Python2 only.

# Python3 Program to check whether a
# given key already exists in a dictionary.

# Function to print sum
def checkKey(dict, key):

    if dict.has_key(key):
        print "Present, value =", dict[key]
    else:
        print "Not present"

# Driver Function
dict = {'a': 100, 'b':200, 'c':300}
key = 'b'
checkKey(dict, key)

key = 'w'
checkKey(dict, key)

Output:

Present, value = 200
Not present