Argument order rules in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the correct order of arguments in a Python function definition?

The correct order is: positional arguments, default arguments, *args (variable positional arguments), keyword-only arguments, and **kwargs (variable keyword arguments).

beginner

Why must positional arguments come before default arguments in Python functions?

Because Python assigns values to arguments in order. If a default argument came before a positional one, Python wouldn't know which value belongs where.

beginner

What happens if you put a default argument before a positional argument in a function definition?

Python will raise a SyntaxError because default arguments must follow positional arguments.

intermediate

What is the role of *args and **kwargs in argument order?

*args collects extra positional arguments as a tuple, and **kwargs collects extra keyword arguments as a dictionary. They must come after positional and default arguments.

intermediate

How do keyword-only arguments fit into the argument order?

Keyword-only arguments come after *args and must be specified by name when calling the function. They can have default values.

Which of the following is the correct order of arguments in a Python function?

A positional, default, *args, keyword-only, **kwargs

B default, positional, *args, **kwargs, keyword-only

C *args, positional, default, **kwargs, keyword-only

D keyword-only, *args, positional, default, **kwargs

The correct order is positional, default, *args, keyword-only, then **kwargs.

What error occurs if a default argument is placed before a positional argument?

A SyntaxError

B TypeError

C ValueError

D NameError

Python raises a SyntaxError if default arguments come before positional arguments.

What does *args collect in a function?

A Only keyword-only arguments

B Extra keyword arguments as a dictionary

C Only default arguments

D Extra positional arguments as a tuple

*args collects extra positional arguments as a tuple.

Where do keyword-only arguments appear in the argument order?

A Before default arguments

B Before positional arguments

C After *args and before **kwargs

D After **kwargs

Keyword-only arguments come after *args and before **kwargs.

Which argument type must be specified by name when calling a function?

A Default arguments

B Keyword-only arguments

C Positional arguments

D *args

Keyword-only arguments must be specified by name when calling the function.

Explain the correct order of arguments in a Python function and why this order matters.

Think about how Python matches values to parameters when you call a function.

Describe the roles of *args and **kwargs in function arguments and their position in the argument order.

Consider how functions handle extra arguments beyond those explicitly named.

Practice

1.

Which of the following correctly describes the order of arguments in a Python function definition?

easy

A. Positional-only, positional-or-keyword, keyword-only

B. Keyword-only, positional-only, positional-or-keyword

C. Positional-or-keyword, keyword-only, positional-only

D. Positional-or-keyword, positional-only, keyword-only

Solution

1. Step 1: Recall argument order rules

   Python functions must define arguments in the order: positional-only, positional-or-keyword, then keyword-only.

2. Step 2: Match the correct order

   Positional-only, positional-or-keyword, keyword-only matches this exact order, others do not.

3. Final Answer:

   Positional-only, positional-or-keyword, keyword-only -> Option A

4. Quick Check:

   Argument order = Positional-only, positional-or-keyword, keyword-only [OK]

Hint: Remember: positional-only first, then normal, then keyword-only [OK]

Common Mistakes:

• Confusing keyword-only and positional-only order
• Thinking positional-or-keyword comes first
• Ignoring positional-only arguments

2.

Which of the following function definitions is syntactically correct in Python?

def example(a, /, b, *, c):
    pass

easy

A. def example(a, /, b, *, c): pass

B. def example(a, b, *, /, c): pass

C. def example(a, *, b, /, c): pass

D. def example(/, a, b, *, c): pass

Solution

1. Step 1: Understand syntax for positional-only and keyword-only

   The slash (/) marks positional-only arguments before it, and the asterisk (*) marks keyword-only arguments after it.

2. Step 2: Check each option's order

   def example(a, /, b, *, c): pass correctly places a before / (positional-only), b as positional-or-keyword, and c after * (keyword-only). Others have invalid order or misplaced / and *.

3. Final Answer:

   def example(a, /, b, *, c): pass -> Option A

4. Quick Check:

   Syntax with / and * correct = def example(a, /, b, *, c): pass [OK]

Hint: Slash (/) before positional-only, star (*) before keyword-only [OK]

Common Mistakes:

• Placing / after positional-or-keyword arguments
• Putting * before /
• Using / as a standalone argument

3.

What is the output of this code?

def func(a, /, b, *, c):
    print(a, b, c)

func(1, 2, c=3)

medium

A. TypeError: missing required keyword-only argument 'c'

B. 1 2 3

C. TypeError: positional argument after keyword argument

D. SyntaxError

Solution

1. Step 1: Understand argument passing

   a is positional-only, so must be passed by position (1). b is positional-or-keyword, passed by position (2). c is keyword-only, passed as c=3.

2. Step 2: Check function call validity and output

   All arguments are passed correctly. The print outputs the values: 1 2 3.

3. Final Answer:

   1 2 3 -> Option B

4. Quick Check:

   func(1, 2, c=3) prints 1 2 3 [OK]

Hint: Positional-only args by position, keyword-only by name [OK]

Common Mistakes:

• Passing positional-only argument by keyword
• Passing keyword-only argument positionally
• Confusing argument order in call

4.

Identify the error in this function call:

def f(x, /, y, *, z):
    return x + y + z

f(x=1, y=2, z=3)

medium

A. No error, returns 6

B. TypeError: missing required positional argument y

C. SyntaxError: invalid function call

D. TypeError: x is positional-only and cannot be passed as keyword

Solution

1. Step 1: Check argument types in definition

   x is positional-only (before /), y is positional-or-keyword, z is keyword-only (after *).

2. Step 2: Analyze function call

   Calling f(x=1, y=2, z=3) tries to pass x by keyword, which is not allowed for positional-only arguments, causing a TypeError.

3. Final Answer:

   TypeError: x is positional-only and cannot be passed as keyword -> Option D

4. Quick Check:

   Positional-only args cannot be keyword = TypeError [OK]

Hint: Positional-only args can't be named in calls [OK]

Common Mistakes:

• Passing positional-only argument by keyword
• Thinking all arguments can be named
• Ignoring the / marker meaning

5.

You want to define a function that takes exactly two positional-only arguments, one positional-or-keyword argument, and two keyword-only arguments. Which of these definitions is correct?

1. def func(a, b, /, c, *, d, e): pass
2. def func(a, /, b, c, *, d, e): pass
3. def func(a, b, c, /, *, d, e): pass
4. def func(a, b, /, *, c, d, e): pass

hard

A. Definition 3

B. Definition 2

C. Definition 1

D. Definition 4

Solution

1. Step 1: Identify argument categories

   Two positional-only args: before / (a, b). One positional-or-keyword: after / and before * (c). Two keyword-only: after * (d, e).

2. Step 2: Check each definition

   Definition 1 matches this order exactly: a, b before /, c after /, d, e after *. Others have wrong placement of / or * or argument counts.

3. Final Answer:

   Definition 1 -> Option C

4. Quick Check:

   Two positional-only, one normal, two keyword-only = Definition 1 [OK]

Hint: Two positional-only before /, one normal after, two keyword-only after * [OK]

Common Mistakes:

• Placing too many args before or after / or *
• Miscounting positional-only arguments
• Confusing keyword-only with positional-or-keyword