lab4

New topics: dictionaries, exceptions, venv

count_vowels(s)

Write a function count_vowels(s) that returns the number of letters a, e, i, o, u, A, E, I, O, U in a given string s (the return value is of type integer).

Examples:

In [ ]: count_vowels('This is a test')
Out[ ]: 4

In [ ]: count_vowels('aoeui')
Out[ ]: 5

In [ ]: count_vowels('aoeuiAOEUI')
Out[ ]: 10

In [ ]: count_vowels('N0 v0w3ls @t @ll ln thls strlng')
Out[ ]: 0

count_chars(s)

Implement a function count_chars(s) which takes a string s and returns a dictionary. The dictionary’s keys are the set of characters that occur in string s. The value for each key is the number of times that this character occurs in the string s.

Examples:

In [ ]: count_chars('x')
Out[ ]: {'x': 1}

In [ ]: count_chars('xxx')
Out[ ]: {'x': 3}

In [ ]: count_chars('xxxyz')
Out[ ]: {'x': 3, 'y': 1, 'z': 1}

In [ ]: count_chars('Hello World')
Out[ ]: {'H': 1, 'e': 1, 'l': 3, 'o': 2, ' ': 1, 'W': 1, 'r': 1, 'd': 1}

count_sub_in_file(filename, s)

Write a function count_sub_in_file(filename, s) that takes two arguments: the substring s (of type string) and a filename (of type string). The function should return the number of occurrences of s in the file given through filename. (Note that each string object has a method count that should be used here.)

You can test your function count_sub_in_file on Alice’s Adventures in Wonderland:

  • How often does the substring “Alice” occur? Expect more than one hundred.

  • How often does the substring “Rabbit” occur? Expect a smaller number.

Modify the function count_sub_in_file(filename, s) so that if the file with name filename cannot be opened, the integer value -1 is returned (instead of the number of substrings s).

traffic_light(load)

A function traffic_light(load) that takes a floating point number load. The function should return the string:

  • “green” for values of load below 0.7.

  • “amber” for values of load equal to or greater than 0.7 but smaller than 0.9

  • “red” for values of load equal to 0.9 or greater than 0.9

Example:

In [ ]: traffic_light(0.5)
Out[ ]: 'green'

venv and rich

  1. Create a virtual environment (using python -m venv venv) and activate the environment

  2. Install the rich python package using pip

  3. Install the cowsay python package using pip

  4. Explore the capabilities of rich and cowsay by running (and inspecting) each of the example programs:

No code needs to be submitted for this task.

Questions:

  • what features of the rich package might be useful for your work (if any)?

pixi and rich (optional)

Optional advanced task if you feel ambitious, and want to learn about pixi.

  • install pixi

  • create a new directory and change into that directory:

    All pixi installation files will be in this directory and below. You can later safely delete this directory and all the contents. You can also inspect the files and (hidden) subdirectories that pixi creates.

  • using the installed pixi tool, install python 3.12 or 3.13, and rich and cowsay.

    Hint: for rich a conda-forge package and a PyPI package exists (so this can be installed as a conda package or via pip). For cowsay there is no conda-package, so this has to be installed via pip.

  • activate the pixi environment (pixi shell) and execute some of the rich examples (such as python emoji.py) check your installation was successful.

    Alternatively, instead of activating the pixi environment, you can also run the program emoji.py through the pixi environment using the command pixi run python emoji.py.

Please submit your file lab4.py for this assignment.

Additional (voluntary) tasks are available in lab4-extra.

End of lab4.