Lecture Notes on Python Argument Passing

Value Types

• Examples: int, float, bool
• Passing by Value:
  • When a value type is passed to a function, a copy is made.
  • Changes made to the parameter inside the function do not affect the original variable.
  • Example:
    • Local variable a is passed as parameter x.
    • Changes to x inside the function don't change a.
    • After function execution, a retains its original value.

Reference Types

• Examples: arrays, lists
• Passing by Reference:
  • A reference to the original value is passed to the function.
  • Changes made to the parameter inside the function persist after the function returns.
  • Example:
    • A list is created and passed to a function.
    • Both external variable and parameter within function point to the same list.
    • Changes to the list inside the function affect the original list.

Detailed Examples

Example 1: Value Type

• Variable a is initialized to 2.
• add5 function is called:
  • Inside add5, x is modified by adding 5.
  • Prints x, which shows 7 (inside function scope).
• After add5 returns, printing a shows it is still 2.

Example 2: Reference Type

• List b is created with [2] at index 0.
• change function is called:
  • Inside change, the list element at index 0 is modified to 10.
  • Prints list showing [10] (inside function scope).
• After change returns, printing b shows [10].

Conclusion

• Understanding the difference between value and reference types is crucial in Python.
• Helps predict how data will transform within functions.