Along with the logical operators AND and OR, there is also an operation called “negation” It changes the logical meaning to the opposite. In programming, negation corresponds to the unary operator
not True # False not False # True
For example, if there's a function that checks if a number is even, then you can use negation to check if a number is odd:
def is_even(number): return number % 2 == 0 print(is_even(10)) # => True print(not is_even(10)) # => False
In the example above, we added
not to the left of the function call and got the opposite action.
Negation is a tool with which you can express intended rules in code without writing new functions.
If you write
not is_even(10), the code will still work:
print(not not is_even(10)) # => True
In logic, double negation means positive:
not not True # True not not False # False print(not not is_even(10)) # => True print(not not is_even(11)) # => False
Now you know what the operators AND, OR and
not mean. They allow you to specify compound conditions with two or more logical expressions.
Implement a function called
is_palindrome()that determines whether a word is a palindrome or not. A palindrome is a word that reads the same way in both directions. Words may be passed to the function in any case, so you must first convert the word to lowercase:
is_palindrome('hut') # true is_palindrome('hexlet') # false is_palindrome('Argument') # true is_palindrome('Function') # false
Implement a function called
is_not_palindrome()which checks if a word is NOT a palindrome:
is_not_palindrome('шалаш') # false is_not_palindrome('Ага') # false is_not_palindrome('хекслет') # true
To do this, call
is_not_palindrome()and apply negation.
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.
By the way, you can participate in courses improvement. There is a link below to the lessons course code which you can edit right in your browser.