create_access_token() takes 0 positional arguments but 1 was given

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Summary

The error create_access_token() takes 0 positional arguments but 1 was given occurs when invoking the create_access_token function with an argument, despite the function being defined with `data: dict** as a keyword-only argument. This is due to a misunderstanding of how Python handles keyword-only arguments and the ****` syntax.

Root Cause

The root cause of this issue is the incorrect usage of the `syntax in the function definition. The ****` syntax is used to indicate that all arguments after it must be specified as keyword arguments. However, when the function is invoked with a positional argument, Python complains that the function takes 0 positional arguments but 1 was given. The key causes are:

  • Misunderstanding of keyword-only arguments
  • Incorrect usage of the `` syntax
  • Failure to pass arguments as keywords

Why This Happens in Real Systems

This issue can occur in real systems when:

  • Developers are not familiar with the `` syntax and its implications
  • Functions are defined with keyword-only arguments, but invoked with positional arguments
  • Code is not thoroughly tested for different invocation scenarios
    Some common scenarios where this might happen include:
  • When working with libraries or frameworks that use keyword-only arguments
  • When defining functions with complex argument structures
  • When invoking functions with a large number of arguments

Real-World Impact

The real-world impact of this issue can be significant, including:

  • Runtime errors: The application may crash or produce unexpected results when the function is invoked incorrectly
  • Security vulnerabilities: Insecure coding practices can lead to security vulnerabilities, especially when working with sensitive data such as authentication tokens
  • Maintenance challenges: Code that is difficult to understand or invoke correctly can lead to maintenance challenges and increased development time

Example or Code

from datetime import datetime, timedelta
import jwt

def create_access_token(**data: dict) -> str:
    to_encode = data.copy()
    expire = datetime.utcnow() + timedelta(minutes=50)
    to_encode.update({"exp": expire})
    encoded_jwt = jwt.JWT().encode(to_encode, "secret_key", alg="HS256")
    return encoded_jwt

# Correct invocation
access_token = create_access_token(sub="user_id")

# Incorrect invocation
try:
    access_token = create_access_token("user_id")
except TypeError as e:
    print(e)

How Senior Engineers Fix It

Senior engineers can fix this issue by:

  • Understanding the ** syntax: Recognizing the implications of using keyword-only arguments and the ** syntax
  • Defining functions correctly: Ensuring that functions are defined with the correct argument structure and syntax
  • Testing thoroughly: Testing code for different invocation scenarios to catch errors early
  • Using type hints and docstrings: Using type hints and docstrings to clearly document function arguments and behavior

Why Juniors Miss It

Junior engineers may miss this issue due to:

  • Lack of experience: Limited experience with Python and its syntax
  • Insufficient training: Inadequate training on keyword-only arguments and the `` syntax
  • Rushed development: Rushing through development without thoroughly testing code
  • Unclear documentation: Unclear or incomplete documentation of function arguments and behavior