Skip to main content
Engineering LibreTexts

16.9: Variables and Parameters Are Local

  • Page ID
    16904
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

    When you create a variable inside a function, it is local, which means that it only exists inside the function. For example:

    def cat_twice(part1, part2):
        cat = part1 + part2
        print_twice(cat)
    

    This function takes two arguments, concatenates them, and prints the result twice. Here is an example that uses it:

    >>> line1 = 'Bing tiddle '
    >>> line2 = 'tiddle bang.'
    >>> cat_twice(line1, line2)
    Bing tiddle tiddle bang.
    Bing tiddle tiddle bang.
    

    When cat_twice terminates, the variable cat is destroyed. If we try to print it, we get an exception:

    >>> print cat
    NameError: name 'cat' is not defined
    

    Parameters are also local. For example, outside print_twice, there is no such thing as bruce.


    This page titled 16.9: Variables and Parameters Are Local is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by Allen B. Downey (Green Tea Press) .

    • Was this article helpful?