Syntaxerror: Positional Argument Follows Keyword Argument

SyntaxError: Positional Argument Follows Keyword Argument — A Complete Guide

Every Python developer, from beginners to seasoned professionals, has encountered the dreaded SyntaxError: positional argument follows keyword argument at least once. This error is one of the most common stumbling blocks when learning how to call functions in Python. Understanding why it occurs, why Python enforces this rule, and how to fix it is essential for writing clean, functional code. In this article, we will break down everything you need to know about this syntax error, complete with examples, explanations, and practical tips to help you avoid it in the future.

What Is This Error?

When you see the message SyntaxError: positional argument follows keyword argument, Python is telling you that in a function call, you placed a positional argument after a keyword argument. Think about it: python requires that all positional arguments come before any keyword arguments in a function call. This is not just a stylistic preference — it is a fundamental rule of Python's syntax The details matter here..

To understand why this rule exists, you first need to grasp the difference between positional arguments and keyword arguments.

Positional Arguments vs. Keyword Arguments

Positional arguments are arguments that are passed to a function based on their position or order. The function matches each argument to its corresponding parameter by where it appears in the call.

Keyword arguments, on the other hand, are arguments that are passed to a function by explicitly specifying the parameter name. This allows you to pass arguments in any order, as long as you name the parameter And that's really what it comes down to..

Consider the following function:

def greet(name, greeting, punctuation):
    print(f"{greeting}, {name}{punctuation}")

A positional argument call would look like this:

greet("Alice", "Hello", "!")

Here, "Alice" maps to name, "Hello" maps to greeting, and "!" maps to punctuation, purely based on order.

A keyword argument call would look like this:

greet(name="Alice", greeting="Hello", punctuation="!")

Or even with mixed ordering:

greet(punctuation="!", name="Alice", greeting="Hello")

The flexibility of keyword arguments is powerful, but it comes with a strict rule: once you use a keyword argument, every argument that follows must also be a keyword argument. You cannot go back to positional arguments after switching to keyword arguments Simple, but easy to overlook..

Why Does Python Enforce This Rule?

The rule exists to eliminate ambiguity. Imagine if Python allowed positional arguments after keyword arguments. Consider this hypothetical scenario:

greet("Alice", greeting="Hello", "!")

In this call, "Alice" is positional, greeting="Hello" is a keyword argument, and "!Here's the thing — " is positional again. In real terms, how would Python know whether "! Also, " should map to greeting or punctuation? Plus, the function definition already has greeting assigned to "Hello", so "! Consider this: " would logically go to punctuation. But the ambiguity itself creates a parsing problem for the interpreter Small thing, real impact. But it adds up..

Python's designers chose to prevent this confusion entirely by enforcing a clear, unambiguous order: all positional arguments first, then all keyword arguments. This makes the code more readable and the interpreter's job simpler.

Common Scenarios That Trigger This Error

Scenario 1: Mixing Arguments in the Wrong Order

The most common cause of this error is simply placing a positional argument after a keyword argument in a function call.

def calculate(a, b, c):
    return a + b + c

result = calculate(a=10, 20, 30)

Running this code will immediately produce:

SyntaxError: positional argument follows keyword argument

The fix is straightforward — convert all arguments to keyword arguments or move the positional arguments before the keyword ones:

result = calculate(10, 20, 30)

or

result = calculate(10, b=20, c=30)

Scenario 2: Using *args and **kwargs Incorrectly

When working with *args and **kwargs, developers sometimes accidentally place positional arguments after keyword unpacking.

def demo(x, y, z):
    print(x, y, z)

args = (1, 2)
demo(x=10, *args)

This will raise the syntax error because *args expands into positional arguments, but it follows the keyword argument x=10. The correct way is:

demo(*args, z=10)

Here, *args provides the first two positional values, and z=10 is the keyword argument Easy to understand, harder to ignore. Nothing fancy..

Scenario 3: Default Parameter Values Combined with Keyword Calls

Another frequent trigger happens when calling a function with default parameters using keyword syntax but then trying to pass additional positional arguments But it adds up..

def process(data, mode="fast", verbose=False):
    pass

process("input.txt", mode="slow", "verbose_output.txt")

The string "verbose_output.txt" is a positional argument placed after the keyword argument mode="slow", which violates Python's syntax rules. The fix is to either use a keyword argument for the third parameter or rearrange the call:

process("input.txt", "verbose_output.txt", mode="slow")

or

process("input.txt", mode="slow", verbose="verbose_output.txt")

(Note: the second example only works if the parameter name matches.)

Scenario 4: Function Calls in Complex Expressions

In more complex code, especially within class methods or nested function calls, this error can be harder to spot Small thing, real impact..

class Builder:
    def construct(self, base, roof, walls):
        pass

builder = Builder()
builder.construct(base="concrete", "wood", walls="brick")

Again, "wood" is positional and follows the keyword argument base="concrete". The solution is to make all arguments keyword-based or reorder them properly.

How to Fix the Error

Fixing this error is simple once you understand the rule. Follow these steps:

1. Identify the function call that triggered the error. Python will point to the exact line in your traceback.
2. Locate the keyword argument that appears before the problematic positional argument.
3. Convert the positional argument to a keyword argument by explicitly naming the parameter, or
4. Move all positional arguments before any keyword arguments in the call.
5. Test the corrected code to ensure it runs without errors.

Here is a quick checklist:

• Are all positional arguments listed before keyword arguments?
• Are *args placed before **kwargs and before any keyword arguments?
• Are you using the correct parameter names for keyword arguments?
• Does the number of arguments match the function's parameter list?

Tips to Avoid This Error in the Future

Consistency is key. Choose a calling convention and stick with it. If you prefer positional arguments, keep them all positional. If you prefer keyword arguments for clarity, use them throughout.

Use IDEs and linters. Modern development environments like PyCharm, VS Code, and tools like `pylint