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Python: Ternary operator

Look at the definition of the function that returns the modulus of the number passed:

def abs(number):
    if number >= 0:
        return number
    return -number

But you can write it more succinctly. To do this, there must be an expression to the right of return, but if is an instruction, not an expression. In Python there is a construction that works like if-else but is considered an expression. It is called the tern operator - the only operator in Python that requires three operands:

def abs(number):
    return number if number >= 0 else -number

The general pattern looks like this: ` if else '.

Let's rewrite the initial version of get_type_of_sentence() in the same way.

It was :

def get_type_of_sentence(sentence):
    last_char = sentence[-1]
    if last_char == '?':
        return 'question'
    return 'normal'


def get_type_of_sentence(sentence):
    last_char = sentence[-1]
    return 'question' if last_char == '?' else 'normal'

print(get_type_of_sentence('Hodor'))   # => normal
print(get_type_of_sentence('Hodor?'))  # => question

You can put a ternary operator into a ternary operator. But you shouldn't do it that way because such code is hard to read and debug.


Implement a function flip_flop() that takes a string as input and, if that string is 'flip', returns the string 'flop'. Otherwise, the function should return 'flip'.

Examples of calls:

print(flip_flop('flip'))  # => 'flop'
print(flip_flop('flop'))  # => 'flip'

Try writing two versions of the function: with the usual if-else, and with the ternary operator.

The exercise doesn't pass checking. What to do? 😶

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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.

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I've read the lessons but nothing is clear 🙄

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  • Ternary operator a way to turn a simple conditional instruction into an expression, such as number if number >= 0 else -number.

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