Argument order rules in Python - Time & Space Complexity

Time Complexity: Argument order rules

O(n)

Understanding Time Complexity

When we write functions, the order of arguments can affect how the function runs, especially when some arguments are optional or have default values.

We want to see how the order of arguments impacts the number of steps the program takes.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

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

greet("Alice")
greet("Bob", "Hi")
greet("Carol", punctuation=".")

This function prints a greeting message using required and optional arguments in a specific order.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: The function call and string formatting happen once per call.
• How many times: Each call runs a fixed number of steps regardless of input size.

How Execution Grows With Input

Explain the growth pattern intuitively.

Input Size (n)	Approx. Operations
1 call	Constant steps (format and print)
10 calls	10 times the constant steps
100 calls	100 times the constant steps

Pattern observation: Each call takes the same amount of work, so total work grows linearly with the number of calls.

Final Time Complexity

Time Complexity: O(n)

This means the total time grows directly with how many times the function is called, not with the argument order itself.

Common Mistake

[X] Wrong: "Changing the order of arguments changes how fast the function runs."

[OK] Correct: The order of arguments affects how you call the function but does not change the number of steps inside the function.

Interview Connect

Understanding argument order helps you write clear code and avoid mistakes, which is a valuable skill in any coding task or interview.

Self-Check

"What if we added a loop inside the function that repeats based on an argument? How would the time complexity change?"

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