Interfacing with SOAP APIs Using XML in Python

SOAP (Simple Object Access Protocol) is a protocol that heavily uses XML for communication between client and server. Python provides powerful libraries like Zeep to work with SOAP APIs, making it easier to send requests, handle responses, and integrate SOAP-based APIs into applications. This tutorial demonstrates how to interface with a SOAP API using Python.

1. What is SOAP?

SOAP is a protocol designed for exchanging structured information in web services. Unlike REST, SOAP relies on XML for message formatting and operates over application layer protocols like HTTP. SOAP messages are composed of:

• Envelope: Defines the start and end of the message.
• Header: Optional, includes metadata.
• Body: Contains the actual data or request.

2. Python Library for SOAP: Zeep

The Zeep library is a powerful tool for interacting with SOAP APIs in Python. It provides an intuitive way to work with WSDL (Web Services Description Language) files and communicate with SOAP endpoints.

3. Example: Fetching Currency Conversion Rates

We’ll use a public SOAP API for this demonstration. The Currency Converter API allows fetching conversion rates between different currencies.

Code Example

from zeep import Client

# WSDL URL for the SOAP API
wsdl_url = "http://www.webservicex.net/CurrencyConvertor.asmx?WSDL"

# Create a Zeep client
client = Client(wsdl=wsdl_url)

# Call the API method
source_currency = "USD"
target_currency = "INR"

try:
    conversion_rate = client.service.ConversionRate(source_currency, target_currency)
    print(f"Conversion rate from {source_currency} to {target_currency}: {conversion_rate}")
except Exception as e:
    print(f"Error occurred: {e}")

Explanation:

• Client(wsdl): Initializes the Zeep client with the WSDL URL of the SOAP API.
• client.service.ConversionRate: Calls the SOAP API method to fetch the conversion rate between the specified currencies.
• Error Handling: Handles exceptions gracefully in case of API errors or network issues.

4. Common Operations with Zeep

• Inspecting API Methods: Use client.wsdl.services to list available services and methods.
• Passing Parameters: Zeep allows passing parameters as Python dictionaries or keyword arguments.
• Debugging Requests: Enable logging to view the raw SOAP requests and responses.

5. Best Practices

• Validate API URLs: Ensure the WSDL URL is accessible and not deprecated.
• Secure Credentials: Use environment variables or secure storage for API credentials.
• Test Error Handling: Simulate network failures and invalid requests to test resilience.

Conclusion

Interfacing with SOAP APIs using Python becomes seamless with libraries like Zeep. Whether you’re fetching currency rates, managing resources, or interacting with enterprise APIs, this approach simplifies communication and enhances productivity. With robust error handling and best practices, you can confidently integrate SOAP APIs into your applications.