Python How to Check if a Key Exists in Dictionary

A Python dictionary is a list of objects that are not in any particular order i.e Unordered.

A dictionary is made up of a collection of key-value pairs. Each key-value pair corresponds to a specific value.

Curly braces { } can be used to describe a dictionary by enclosing a comma-separated list of key-value pairs.

Every key is separated from its associated value by a colon “:”.

Given a dictionary, the task is to determine whether the given key exists in the dictionary.

Examples:

Input :

dictionary = {'This': 100, 'is':200, 'python':300} , key = is

Output:

Yes

Check whether given Key already exists in a Python Dictionary

There are several ways to check whether the given key exists in the dictionary some of them are:

Using keys() function
Using if-in Statements
Using List and if statement
Using Exceptional Handling
Using get() function
Using ‘if not in’ statement

Method #1: Using keys() function

The keys() method returns a list of all the available keys in the dictionary. Using the inbuilt method keys(), use an if statement and the ‘in’ operator to determine whether or not the key exists in the dictionary.

# Given Dictionary

dictionary = {'this': 100, 'is': 200, 'python': 300}

# Given key
key = 'is'

# Checking if key is exist in dictionary using keys() method
if key in dictionary.keys():
  # If the key exits then print yes
    print("Yes")
# If the  key do not exist then print no
else:
    print("No")

Output:

Yes

Method #2: Using if-in Statements

To verify if a key exists in the dictionary, we can use the ‘in operator’ directly with the dictionary.

The expression:

key in dictionary

If the key exists in the dictionary, it will evaluate to True; otherwise, it will evaluate to False.

Let’s use this to see if the key is in the dictionary.

# Given Dictionary

dictionary = {'this': 100, 'is': 200, 'python': 300}

# Given key
key = 'is'

# Using if and in to check whether the key is present in dictionary
if key in dictionary:
  # If the key exits then print yes
    print("Yes")
# If the  key do not exist then print no
else:
    print("No")

Output:

Yes

Method #3: Using List and if statement

Convert the dictionary keys to list.
Check if the key present in this list using if statement.

Below is the implementation:

# Given Dictionary
dictionary = {'this': 100, 'is': 200, 'python': 300}

# Given key
key = 'is'
# Converting dictionary keys to list
keyslist = list(dictionary.keys())

# Checking if key is exist in list using if
if key in keyslist:
  # If the key exits then print yes
    print("Yes")
# If the  key do not exist then print no
else:
    print("No")

Output:

Yes

Method #4: Using Exceptional Handling

It will raise a KeyError if we try to access a value of key that does not exist in the dictionary. This can also be used to see if anything exists in the dict.

This can also be a way to check if exist in dictionary or not .

Below is the implementation:

# Given Dictionary
dictionary = {'this': 100, 'is': 200, 'python': 300}

# Given key
key = 'is'
# Using try and except
try:
    # If the key exist in dictionary its value is assigned to test and then it prints yes
    test = dictionary[key]
    print("Yes")
# If the key do not exist in dictionary it prints no
except KeyError:
    print("No")

Output:

Yes

Method #5: Using get() function

The dict class in Python has a get() method that accepts a key and a default value.

dictionary.get(keyname, value)

The function’s behaviour,

If the given key is found in the dictionary, it returns the value associated with that key.
If the given key does not exist in the dictionary, the passed default value argument is returned.
If the given key does not exist in the dictionary and the default value is not provided, it returns None.

Below is the implementation:

# Given Dictionary
dictionary = {'this': 100, 'is': 200, 'python': 300}

# Given key
key = 'is'
# Using get()
if dictionary.get(key) is not None:
    print("Yes")
else:
    print("No")

Output:

Yes

Method #6 : Using ‘if not in’ statement

We’ve just verified whether the key exists in the dictionary so far.

However, if we want to verify if a key does not exist in the dictionary, we can use ‘if not in’ with the dictionary directly.

Below is the implementation:

# Given Dictionary
dictionary = {'this': 100, 'is': 200, 'python': 300}

# Given key
key = 'is'
# Using if not in
if key not in dictionary:
  # if the key not in dictionary then we print no
    print("No")
else:
    print("Yes")

Output:

Yes

Related Programs: