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8.5: List Slices

  • Page ID
    8622
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

    The slice operator also works on lists:

    >>> t = ['a', 'b', 'c', 'd', 'e', 'f']
    >>> t[1:3]
    ['b', 'c']
    >>> t[:4]
    ['a', 'b', 'c', 'd']
    >>> t[3:]
    ['d', 'e', 'f']

    If you omit the first index, the slice starts at the beginning. If you omit the second, the slice goes to the end. So if you omit both, the slice is a copy of the whole list.

    >>> t[:]
    ['a', 'b', 'c', 'd', 'e', 'f']

    Since lists are mutable, it is often useful to make a copy before performing operations that fold, spindle, or mutilate lists.

    A slice operator on the left side of an assignment can update multiple elements:

    >>> t = ['a', 'b', 'c', 'd', 'e', 'f']
    >>> t[1:3] = ['x', 'y']
    >>> print(t)
    ['a', 'x', 'y', 'd', 'e', 'f']

    This page titled 8.5: List Slices is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by Chuck Severance.

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