Python Check if key exists in JSON and iterate the JSON array

In this article, we will see how to perform the following JSON operations using Python.

• Check if the key exists or not in JSON.
• Check if there is a value for a key, and return a default value if the key is missing
• Iterate JSON array

Let’s see each one by one.

Check if the key exists or not in JSON

Let’s assume you received the following student, JSON. And you wanted to check if the percentage key is present or not in JSON data. if it is present directly access its value instead of iterating the entire JSON.

student ={ 
   "id":1,
   "name":"john wick",
   "class":8,
   "percentage":75,
   "email":"jhon@pynative.com"
}

Example:

import json

studentJson ="""{
   "id": 1,
   "name": "john wick",
   "class": 8,
   "percentage": 75,
   "email": "jhon@pynative.com"
}"""

print("Checking if percentage key exists in JSON")
student = json.loads(studentJson)
if "percentage" in student:
    print("Key exist in JSON data")
    print(student["name"], "marks is: ", student["percentage"])
else:
    print("Key doesn't exist in JSON data")

Output:

Checking if percentage key exists in JSON
Key exist in JSON data
john wick marks is:  75

Check if there is a value for a key in JSON

We need a value of the key to be present in JSON so we can use this value in our system. In this case, we need to be sure that value is present for a key, and if it is none or not present, we use the default value.

Example to check if there is a value for a key in JSON

import json

studentJson ="""{
   "id": 1,
   "name": "john wick",
   "class": null,
   "percentage": 75,
   "email": "jhon@pynative.com"
}"""

if not (student.get('email') is None):
     print("value is present for given JSON key")
     print(student.get('email'))
else:
    print("value is not present for given JSON key")

Output:

value is present for given JSON key
jhon@pynative.com

Return default value if the key is missing

Let’s see how to use a default value if the value is not present for a key. As you know, the json.loads method converts JSON data into Python dict so we can use the get method of dict class to assign a default value to the key if the value is missing.

import json

studentJson ="""{
   "id": 1,
   "name": "john wick",
   "class": null,
   "percentage": 75,
   "email": "jhon@pynative.com"
}"""

if not (student.get('subject') is None):
    print("value is present for given JSON key")
    print(student.get('subject'))
else:
    print("using a default value for a given key")
    print(student.get('subject', 'Science'))

Output

value is not present for given JSON key
using a default value for a given key
Science

Python Find if the nested key exists in JSON

Most of the time, JSON contains so many nested keys. Let’s see how to access nested key-value pairs from JSON directly. Let’s assume you have the following JSON data. and you want to check and access the value of nested key marks.

{ 
   "class":{ 
      "student":{ 
         "name":"jhon",
         "marks":{ 
            "physics":70,
            "mathematics":80
         }
      }
   }
}

Example 1: Access nested key directly

If you know that you always have the parent key present, then you can access the nested JSON key directly. In this case, we always have ‘class‘ and ‘student‘ keys so we can access nested key marks directly.

import json

sampleJson = """{ 
   "class":{ 
      "student":{ 
         "name":"jhon",
         "marks":{ 
            "physics":70,
            "mathematics":80
         }
      }
   }
}"""

print("Checking if nested JSON key exists or not")
sampleDict = json.loads(sampleJson)
if 'marks' in sampleDict['class']['student']:
    print("Student Marks are")
    print("Printing nested JSON key directly")
    print(sampleDict['class']['student']['marks'])

Output

Checking if nested JSON key exists or not
Student Marks are
Printing nested JSON key directly
{'physics': 70, 'mathematics': 80}

Example 2: Access nested key using nested if statement

If you are not sure whether you always have the parent key present, in such cases, we need to access nested JSON using nested if statement, to avoid any exceptions.

import json

sampleJson = """{ 
   "class":{ 
      "student":{ 
         "name":"jhon",
         "marks":{ 
            "physics": 70,
            "mathematics": 80
         }
      }
   }
}"""

print("Checking if nested JSON key exists or not")

if 'class' in sampleDict:
    if 'student' in sampleDict['class']:
        if 'marks' in sampleDict['class']['student']:
            print("Printing nested JSON key-value")
            print(sampleDict['class']['student']['marks'])

Output:

Iterate JSON Array

Many times nested JSON key contains a value in the form of an array or dictionary. In this case, if you need all values, we can iterate the nested JSON array. Let’s see the example.

import json

sampleJson = """{ 
   "class":{ 
      "student":{ 
         "name":"jhon",
         "marks":{ 
            "physics": 70,
            "mathematics": 80
         },
         "subjects": ["sub1", "sub2", "sub3", "sub4"]
      }
   }
}"""

if 'class' in sampleDict:
    if 'student' in sampleDict['class']:
        if 'subjects' in sampleDict['class']['student']:
            print("Iterating JSON array")
            for sub in sampleDict['class']['student']['subjects']:
                print(sub)

Output:

Iterating JSON array
sub1
sub2
sub3
sub4