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11.8: Regular Expressions (Exercises)

  • Page ID
    8665
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)

    Exercise 1: Write a simple program to simulate the operation of the grep command on Unix. Ask the user to enter a regular expression and count the number of lines that matched the regular expression:

    $ python grep.py
    Enter a regular expression: ^Author
    mbox.txt had 1798 lines that matched ^Author
    
    $ python grep.py
    Enter a regular expression: ^X-
    mbox.txt had 14368 lines that matched ^X-
    
    $ python grep.py
    Enter a regular expression: java$
    mbox.txt had 4218 lines that matched java$

    Exercise 2: Write a program to look for lines of the form

    `New Revision: 39772`

    and extract the number from each of the lines using a regular expression and the findall() method. Compute the average of the numbers and print out the average.

    Enter file:mbox.txt
    38549.7949721
    
    Enter file:mbox-short.txt
    39756.9259259

    11.8: Regular Expressions (Exercises) is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by Chuck Severance.

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