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Python: Named arguments

In this lesson, we'll look at what parameters exist, how they differ, and when to apply them.

Arguments are data that are passed to a function call. They come in two types:

The first type is positional arguments. They are passed in the same order as the function parameters are defined:

# (text, length)
truncate('My Text', 3)

The second type is named arguments. They are passed not just as values, but as a pair "name=value". So you can pass them in any order:

# Arguments are passed in a different order
truncate(length=3, text='My Text')

If you look carefully at the two examples above, you can see that they are two identical functions.

Now let's see when to apply these types of arguments.

The type of parameter you choose depends on who is calling the function.

There are two reasons to use named arguments:

  • They increase readability because you can see the names at a glance

  • You can leave out all the intermediate parameters that we don't need right now

The latter is useful if the function has many optional parameters. Let's look at an example:

def print_params(a=1, b=2, c=None, d=4):
    print(a, b, c, d)

# You only need to pass d, but you have to pass all
f(1, 2, 3, 8)

# Named arguments allow you to pass only d
# Default values are used for the other arguments

Named arguments can be passed at the same time as positional arguments. Then positional arguments must go at the beginning:

# Transmit only a (positional) and d (as named)
f(3, d=3)


Implement a function trim_and_repeat() that takes three parameters: the string, offset - the number of characters by which to trim the string to the left and repetitions - the number of times it needs to be repeated, and returns the resulting string.
The default number of characters to cut is 0, and the number of repetitions is 1.

text = 'python'
print(trim_and_repeat(text, offset=3, repetitions=2)) # => honhon
print(trim_and_repeat(text, repetitions=3)) # => pythonpythonpython
print(trim_and_repeat(text)) # => python
The exercise doesn't pass checking. What to do? 😶

If you've reached a deadlock it's time to ask your question in the «Discussions». How ask a question correctly:

  • Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.
In my environment the code works, but not here 🤨

Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.

My code is different from the teacher's one 🤔

It's fine. 🙆 One task in programming can be solved in many different ways. If your code passed all tests, it complies with the task conditions.

In some rare cases, the solution may be adjusted to the tests, but this can be seen immediately.

I've read the lessons but nothing is clear 🙄

It's hard to make educational materials that will suit everyone. We do our best but there is always something to improve. If you see a material that is not clear to you, describe the problem in “Discussions”. It will be great if you'll write unclear points in the question form. Usually, we need a few days for corrections.

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