5.7 Passing Lists to Functions

Passing an Entire List to a Function

In [1]:
def modify_elements(items):
    """"Multiplies all element values in items by 2."""
    for i in range(len(items)):
        items[i] *= 2
In [2]:
numbers = [10, 3, 7, 1, 9]
In [3]:
modify_elements(numbers)
In [4]:
numbers
Out[4]:
[20, 6, 14, 2, 18]

Passing a Tuple to a Function

  • When you pass a tuple to a function, attempting to modify the tuple’s immutable elements results in a TypeError.
In [5]:
numbers_tuple = (10, 20, 30)
In [6]:
numbers_tuple
Out[6]:
(10, 20, 30)
In [7]:
modify_elements(numbers_tuple)

------------------------------------------------------------------------
TypeError                              Traceback (most recent call last)
<ipython-input-7-9339741cd595> in <module>
----> 1 modify_elements(numbers_tuple)

<ipython-input-1-aa30cff7ee99> in modify_elements(items)
      2     """"Multiplies all element values in items by 2."""
      3     for i in range(len(items)):
----> 4         items[i] *= 2

TypeError: 'tuple' object does not support item assignment

A Note Regarding Tracebacks

  • A traceback shows code that led to an exception.
  • When an exception occurs in a single-line snippet, it’s always preceded by ----> 1, indicating that line 1 (the snippet’s only line) caused the exception.
  • Multiline snippets like a function definition show consecutive line numbers starting at 1.
  • The last line of code shown with ----> caused the exception.

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