[Tutor] difference between expressions and statements

[Ben Finney]

Jared Nielsen <nielsen.jared at gmail.com> writes:

> Could someone explain the difference between expressions and
> statements?

For general programming terminology, the Wikipedia articles tend to be
good.

<URL:https://en.wikipedia.org/wiki/Expression_%28computer_science%29>
<URL:https://en.wikipedia.org/wiki/Statement_%28computer_science%29>

Roughly:

* An expression evaluates to some single value.

* A statement does some action.

> I know that expressions are statements that produce a value.

Expressions are not statements. A statement *may* be an expression.

Statements in Python can consist of an expression, or can consist of
other things.

> I'm unclear on functions and especially strings.

You're looking for a strict dichotomy which doesn't exist, and I think
that's confusing you.

> Are any of the following expressions?

They can all be statements.

> print(42)
> print("spam")

These are function calls. A function call evaluates to a value, so is
always an expression.

> spam = 42

Assignment is only a statement in Python. The statement is an
instruction to perform the assignment.

The left side is an expression evaluating to a reference; the right side
is an expression evaluating to a value.

> Is a variable assignment considered a value?

In Python, assignment (try not to think in terms of “variable”;
assignment is the act of binding a reference to a value) is always a
statement.

In other languages, assignment can return a value and is therefore an
expression. That is not the case in Python.

> Is the first example producing a value or simply displaying an
> integer?
> Does a string count as a value?

Yes to all these.

Learn more about statements – especially the fact that statements
consist sometimes of expressions alone, sometimes of other things
including expressions – at the Python Language Reference
<URL:https://docs.python.org/3/reference/expressions.html>
<URL:https://docs.python.org/3/reference/simple_stmts.html>.

-- 
 \         “If nature has made any one thing less susceptible than all |
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Ben Finney