Extracting Receipt Data using GPT-4 and Python¶

This post demonstrates how to use Python's Pydantic library and OpenAI's GPT-4 model to extract receipt data from images and validate the total amount. This method is particularly useful for automating expense tracking and financial analysis tasks.

Defining the Item and Receipt Classes¶

First, we define two Pydantic models, Item and Receipt, to structure the extracted data. The Item class represents individual items on the receipt, with fields for name, price, and quantity. The Receipt class contains a list of Item objects and the total amount.

class Item(BaseModel):
    name: str
    price: float
    quantity: int


class Receipt(BaseModel):
    items: list[Item]
    total: float

Validating the Total Amount¶

To ensure the accuracy of the extracted data, we use Pydantic's model_validator decorator to define a custom validation function, check_total. This function calculates the sum of item prices and compares it to the extracted total amount. If there's a discrepancy, it raises a ValueError.

@model_validator(mode="after")
def check_total(cls, values: "Receipt"):
    items = values.items
    total = values.total
    calculated_total = sum(item.price * item.quantity for item in items)
    if calculated_total != total:
        raise ValueError(
            f"Total {total} does not match the sum of item prices {calculated_total}"
        )
    return values

Extracting Receipt Data from Images¶

The extract_receipt function uses OpenAI's GPT-4 model to process an image URL and extract receipt data. We utilize the instructor library to configure the OpenAI client for this purpose.

import instructor
from openai import OpenAI

client = instructor.from_openai(
    client=OpenAI(),
    mode=instructor.Mode.TOOLS,
)


def extract(url: str) -> Receipt:
    return client.chat.completions.create(
        model="gpt-4",
        max_tokens=4000,
        response_model=Receipt,
        messages=[
            {
                "role": "user",
                "content": [
                    {
                        "type": "image_url",
                        "image_url": {"url": url},
                    },
                    {
                        "type": "text",
                        "text": "Analyze the image and return the items in the receipt and the total amount.",
                    },
                ],
            }
        ],
    )

Practical Examples¶

In these examples, we apply the method to extract receipt data from two different images. The custom validation function ensures that the extracted total amount matches the sum of item prices.

urls = [
    "https://templates.mediamodifier.com/645124ff36ed2f5227cbf871/supermarket-receipt-template.jpg",
    "https://ocr.space/Content/Images/receipt-ocr-original.jpg",
]

for url in urls:
    receipt = extract(url)
    print(receipt)

By combining the power of GPT-4 and Python's Pydantic library, we can accurately extract and validate receipt data from images, streamlining expense tracking and financial analysis tasks.