Python: Function call - expressions
Let's continue to look at functions and their components. Today, it's time to look at expressions. Let's consider what it is and whether a function call can be mistaken for an expression.
An expression in programming returns a result that can be used. You probably already know a lot about expressions and the principles by which they're constructed. For example, mathematical operations like addition and subtraction, string operations like concatenation are all expressions:
1 + 5 * 3
'He' + 'Let'
# Variables can be part of an expression
rate * 5
The peculiarity of expressions is that they return a result that can be used again: for example, they can be assigned to a variable or printed. This is what it looks like in the code:
# Here the expression is 1 + 5
sum = 1 + 5
print(1 + 5)
But not everything in programming is an expression. The definition of a variable is an instruction, which means it cannot be part of an expression. In other words, this code will lead to an error:
# Meaningless code that won't work
10 + sum = 1 + 5
Now let's see if a function call can be taken as an expression.
We know that functions return results, therefore they're expressions. This leads to a lot of interesting possibilities. For example, we can use a function call directly in mathematical operations. This is how we can get the last character index in a word:
name = 'python'
# Indexes start with zero
# Function call and subtraction together!
last_index = len(name) - 1
print(last_index) # => 5
This code has no new syntax. We have merely connected parts we already know, we're relying on their nature. We could go even further:
print(len(name) - 1) # => 5
All of this applies for any function, e.g., string functions:
name = 'python'
# Interpolation is used
print(f'Last character: {name[len(name) - 1]}')
# 'Last character: n'
As you will see next, expressions can be combined to produce increasingly complex behavior in different places and in any way. The more you learn and practice Python, the better you will understand expressions. Over time, you'll learn how to connect the pieces of code to get the results you want.
Instructions
Display the first and last letters of the sentence written in the text variable in the following format:
First: N Last: t
Try to create only one variable to be assigned to the text to before you print it. In this lesson, we're practicing building a compound expression.
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 🙄
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