Fixing ValueError
When Using read_json
in Pandas
The error ValueError: Expected object or value
occurs when using pd.read_json()
in Pandas to read a JSON file or JSON lines file, and the file is improperly formatted or empty. This article explains the causes and solutions to resolve this error effectively.
Why Does This Error Occur?
The ValueError: Expected object or value
is typically caused by:
- An empty file or string passed to
pd.read_json()
. - Malformed JSON content (e.g., missing brackets, incorrect syntax).
- Using the wrong format option when reading JSON lines (
lines=True
).
Example of the Error
Consider the following malformed or empty JSON file named data.json
:
# Malformed or empty JSON content
When attempting to read this file with pd.read_json()
:
import pandas as pd
# Attempt to read an empty or malformed JSON file
df = pd.read_json('data.json')
Output:
ValueError: Expected object or value
How to Fix the Error
1. Ensure the JSON File is Not Empty
Check if the file contains valid JSON data. For example, the content of data.json
should look like this:
[
{"Name": "Alice", "Age": 25, "Gender": "Female"},
{"Name": "Bob", "Age": 30, "Gender": "Male"}
]
Then, read the JSON file using:
df = pd.read_json('data.json')
print(df)
Output:
Name Age Gender
0 Alice 25 Female
1 Bob 30 Male
2. Check for Proper JSON Syntax
Ensure the JSON file has the correct structure. For instance, if the file contains multiple JSON objects, it should either be wrapped in a list or written as JSON lines (one object per line).
3. Reading JSON Lines Format
If your file contains JSON objects written in JSON lines format (one object per line), use the lines=True
parameter:
# Example of JSON lines file (data.jsonl)
{"Name": "Alice", "Age": 25, "Gender": "Female"}
{"Name": "Bob", "Age": 30, "Gender": "Male"}
df = pd.read_json('data.jsonl', lines=True)
print(df)
Output:
Name Age Gender
0 Alice 25 Female
1 Bob 30 Male
4. Validate the File Before Loading
Use Python’s json
module to validate the JSON content before loading it into Pandas:
import json
# Validate JSON content
with open('data.json', 'r') as file:
data = json.load(file)
print(data)
# Load into Pandas
df = pd.DataFrame(data)
print(df)
5. Handle Malformed or Partial JSON
If the JSON file is malformed, use jsonlines
library or manually preprocess the file to remove errors:
import jsonlines
# Reading a malformed JSON lines file
with jsonlines.open('data.jsonl') as reader:
data = [obj for obj in reader]
df = pd.DataFrame(data)
print(df)
Conclusion
The ValueError: Expected object or value
error in Pandas often results from an empty or improperly formatted JSON file. By ensuring the file contains valid JSON data, using the correct parameters for JSON lines, or validating the content before reading, you can successfully load JSON data into Pandas for analysis.