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2017, Apr 10 - Dimitri Merejkowsky
License: CC By 4.0

For quite some time I've been adding a file called `ui.py` in some of the Python projects I was working on.

Since I believe in the rule of three[1] and I already have three different projects using it, I've decided to share it to the world.

1: https://blog.codinghorror.com/rule-of-three/

Feel free to take a look at the github page[2].

2: https://github.com/dmerejkowsky/python-cli-ui

What it does

Let's start with a screen shot:

ui demo [IMG]

Coloring

It's a module to write colorful command line interfaces in Python.

It's a tiny wrapper on top of `colorama`, with a (IMHO) nicer API than crayons[3] or lazyme[4].

3: https://pypi.python.org/pypi/crayons

4: https://pypi.python.org/pypi/lazyme

Here's an example:

ui.info(ui.red, "Error", ui.reset, ui.bold, file_path, ui.reset, "not found")

This will print the word 'Error' in red, the file path in bold, and the 'not found' normally.

The API follows the behavior of the `print()` function: by default, tokens are separated by spaces, `\n` is added at the end, and you can specify your own `sep` and `end` keywords if you need to.

Displaying enumerations

It also allows to display items of a list, taking care of "off-by-one" errors and aligning the numbers nicely (note the leading space for `1/12`)

>>> months = ["January", "February", ..., "December"]
>>> for i, month in enumerate(months):
>>>     ui.info_count(i, 12, month)

	( 1/12) January

	( 2/12) February


...

	(12/12) December

Indenting

>>> first_name = "John"
>>> last_name = "Doe"
>>> adress = """\
ACME Inc.
795 E Dragram
Tucson AZ 85705
USA
"""
>>> ui.info("People")
>>> ui.info(ui.tabs(1), first_name, last_name)
>>> ui.info(ui.tabs(1), "Adress:")
>>> ui.info(ui.indent(2, adress))
People:
  John Doe
  Adress:
    795 E Dragram
    Tucson AZ 85705
    USA

Unicode goodness

You can define your own suite of characters, which will get a color, a unicode and an ASCII representation (so that it works on Windows too.)

For instance:

check  = UnicodeSequence(green, "✓", "ok")

ui.info("Success!", ui.check)

On Linux:

unicode check [IMG]

On Windows:

ascii check [IMG]

Semantics

The module also contains "high-level" methods such as `info_1`, `info_2`, `info_3`, so that you can write:

ui.info_1("Making some tea")
...
ui.info_2("Boiling water")
...
ui.info_3("Turning kettle on")
...
ui.info_1("Done")

Which will be rendered as:

python ui cli example [IMG]

This allows you to group your messages in a coherent way. Here the main message is 'Making some tea'. 'Boiling water' is a sub-task of making the tea, and 'Turning the kettle on' is a sub-task of the boiling water process.

In the same vein, `warning`, `error` and `fatal` methods are provided for when things go wrong. (The last one calls `sys.exit()`, hence the name)

There's also a `debug` function, for messages you are only interested when debugging: you can control the verbosity using the `CONFIG` global dictionary.

ui.CONFIG['quiet'] = True
ui.info("this is some info") # won't get printed

ui.CONFIG['verbose'] = True
ui.debug("A debug message") # will get printed

Interaction

Arbitrary string with a default

>>> domain = ui.ask_string("Please enter your domain name", default="example.com")
>>> print("You chose:", domain)
> Please enter your domain name (example.com)
(nothing)
> You chose example.com

>>> domain = ui.ask_string("Please enter your domain name", default="example.com")
>>> print("You chose:", domain)
> Please enter your domain name (example.com)
foobar.com
> You chose foobar.com

Boolean choice

Note how the prompt goes from `Y/n` (y uppercase), to `y/N` (n uppercase) depending on the default value:

>>> with_sugar = ui.ask_yes_no("With sugar?", default=True)
> "With sugar ? (Y/n)"
n
> False

>>> with_cream = ui.ask_yes_no("With cream?", default=False)
> "With cream? (y/N)"
(nothing)
> False

Choice in a list

Note how the user is stuck in a loop until he enters a valid answer, and how the first item is selected by default:

>>> choices = ["apple", "orange", "banana"]
>>> answer = ui.ask_choice("Select a fruit:", choices)
> Select a fruit:
1. apple (default)
2. orange
3. banana
> foobar
Please enter a number between 1 and 3
> 4
Please enter a number between 1 and 3
> 2
>>> print(answer)
oranges

Other goodies

A timer

@ui.timer("Doing foo")
def foo():
     # something that takes time

>>> foo()
... # output of the foo method
Doing foo took 3min 13s

Works also in a `with` statement:

with ui.timer("making foobar"):
    foo()
    bar()

Did you mean?

>>> commands = ["install", "remove"]
>>> user_input = input()
intall
>>> ui.did_you_mean("No such command", user_input, choices)
No such command.
Did you mean: install?

A pytest fixture

You can also write tests to assert that a certain message matching a regexp was emitted.

def say_hello(name):
    ui.info("Hello", name)

def test_say_hello(messages):
    say_hello("John")
    assert messages.find(r"Hello\w+John")

Parting words

Well, I hope you'll find this module useful.

It is available as `python-cli-ui` on pypi

Cheers!

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