[Tutor] difference between expressions and statements

[Jared Nielsen]

Thanks for the thorough answer, Bob. I now understand the difference.
On Apr 10, 2014 2:11 PM, "bob gailer" <bgailer at gmail.com> wrote:

> Caveat: I began this before there were any other responses. So this may be
> overkill - but I ike to be thorough.
>
> On 4/9/2014 12:49 PM, Jared Nielsen wrote:
>
>> Hi Pythons,
>> Could someone explain the difference between expressions and statements?
>>
>>> I know that expressions are statements that produce a value.
>>>
>> No. Expressions are not statements. These are mutually exclusive.
>> Expressions do produce values.
>>
> An attempt at a thorough answer:
>
> In the language reference glossary under "expression" you will find:
>
> "A piece of syntax which can be evaluated to some value. In other words,
> an expression is an accumulation of expression elements like literals,
> names, attribute access, operators or function calls which all return a
> value.... There are also statements which cannot be used as expressions,
> such as if. Assignments are also statements, not expressions."
>
> Tthe above is a quote; I don't like some of the grammar.
>
> In your examples print is a function. So all calls to print are
> expressions.
>
> In the language reference you will also find:
>
> 7. Simple statements
> 7.1. Expression statements
> 7.2. Assignment statements
> 7.3. The assert statement
> 7.4. The pass statement
> 7.5. The del statement
> 7.6. The return statement
> 7.7. The yield statement
> 7.8. The raise statement
> 7.9. The break statement
> 7.10. The continue statement
> 7.11. The import statement
> 7.12. The global statement
> 7.13. The nonlocal statement
> 8. Compound statements
> 8.1. The if statement
> 8.2. The while statement
> 8.3. The for statement
> 8.4. The try statement
> 8.5. The with statement
> 8.6. Function definitions
> 8.7. Class definitions
>
> With the exception of
> - 7.1. Expression statements
> - all of the above are either start with a keyword except 7.2 assignment
> which is indicated by an equal sign (=) .
> - all of the above cause something to happen (except pass), and do not
> return a value.
>
> 7.1. Expression statement is either one expression or several separated by
> commas.
> Used interactively to display value(s).
> Used anywhere to make a function call.
>
>> I'm unclear on functions and especially strings.
>> Are any of the following expressions?
>>
>> print(42)
>> print("spam")
>> spam = 42
>> print(spam)
>>
>> Is the first example producing a value or simply displaying an integer?
>>
> All function calls return a value. In the case of print the return value
> is always None.
> spam = 42 is a statement. (indicated by the = sign. 42 is a value.
>
>> Does a string count as a value?
>> Yes - however I suspect you are limiting "string" to something within
>> quotes. Those are "string literals".
>> Is a variable assignment considered a value?
>>
> No
>
>> If I print a variable is that considered production of a value?
>>
> See above comment on print.
>
> Long but comprehensive answer. Feel free to ask questions.
>
> Note there are various subtleties here -some  keywords may be used to
> start a statement or in an expression - e.g. if, else, for yield.
>
> This also raises the fact that else (inter ala) is neither an expression
> or a statement; rather it is part of a compound statement. Nothing is
> simple.
>
> Oh there is more but I may never hit send....
>
>
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