Given two list of dictionaries, the task is to merge these two lists of dictionaries based on some value.

Method #1: Using defaultdict and extend to merge two list of dictionaries based on school_id.

# Python code to merge two list of dictionaries
# based on some value.

from collections import defaultdict

# List initialization
Input1 = [{'roll_no': ['123445', '1212'], 'school_id': 1},
		{'roll_no': ['HA-4848231'], 'school_id': 2}]

Input2 = [{'roll_no': ['473427'], 'school_id': 2},
		{'roll_no': ['092112'], 'school_id': 5}]


# Using defaultdict
temp = defaultdict(list)

# Using extend
for elem in Input1:
	temp[elem['school_id']].extend(elem['roll_no'])

for elem in Input2:
	temp[elem['school_id']].extend(elem['roll_no'])

Output = [{"roll_no":y, "school_id":x} for x, y in temp.items()]

# printing
print(Output)

Output:

[{‘school_id’: 1, ‘roll_no’: [‘123445’, ‘1212’]}, {‘school_id’: 2, ‘roll_no’: [‘HA-4848231’, ‘473427’]}, {‘school_id’: 5, ‘roll_no’: [‘092112’]}]

Method #2: Using extend() only.

# Python code to merge two list of dictionaries
# based on some value.

# List initialization
Input1 = [{'roll_no': ['123445', '1212'], 'school_id': 1},
		{'roll_no': ['HA-4848231'], 'school_id': 2}]
Input2 = [{'roll_no': ['473427'], 'school_id': 2},
		{'roll_no': ['092112'], 'school_id': 5}]

# Iterating and using extend to convert
for elm2 in Input2:

	for elm1 in Input1:
		if elm2['school_id'] == elm1['school_id']:
			elm1['roll_no'].extend(elm2['roll_no'])
			break
	else:
		Input1.append(elm2)

# printing
print(Input1)

Output:

[{‘school_id’: 1, ‘roll_no’: [‘123445’, ‘1212’]}, {‘school_id’: 2, ‘roll_no’: [‘HA-4848231’, ‘473427’]}, {‘school_id’: 5, ‘roll_no’: [‘092112’]}]