A question about comma in Python

[mocqueanh]

this is a Python source file:


print "Hi", age=int(raw_input("How old are you? "))

When i run it by Python IDLE, i receive: Syntax Error: Invalid Syntax

But if i put age with a new line, i can run it


print "Hi",
age=int(raw_input("How old are you?"))

Why ? I think a comma ( , ) is use to suppress new line in Python, so there is no diffrence between them above.

[xtacocorex]

You're trying to get user input while outputting (print statement) to the screen at the same time. I belive that doesn't work. I can't do that in FORTRAN or C++ because of how reads and writes are, Python should follow the same rule.

I may be wrong here and welcome any Python expert to jump in and save me from imparting wrong wisdom.

[bashologist]

>>> age = raw_input("How old are you? ")
How old are you? 21
>>> print "Hi", age
Hi 21
>>>

Hi 21?!

[cwaldbieser]

You're trying to get user input while outputting (print statement) to the screen at the same time. I belive that doesn't work. I can't do that in FORTRAN or C++ because of how reads and writes are, Python should follow the same rule.

I may be wrong here and welcome any Python expert to jump in and save me from imparting wrong wisdom.

This is not correct.


print "Hi", int(raw_input("How old are you? "))

The above will actually work just fine.

The problem with the original syntax is that assignment is a statement in Python. It is not treated as an expression (like in C or Javascript, for example). This is to thwart a common mistake in programming:


if(x = 7) //Oops! Assignment. This will always evaluate to a true value!
{
alert("X is lucky seven!");
}

[xtacocorex]

Thanks cwaldbieser for the clarification. I'm not a Python programmer and was going with my knowledge of other languages.

[duff]

Why ? I think a comma ( , ) is use to suppress new line in Python, so there is no diffrence between them above.

Because Python uses a line break to separate statements.

print "Hi", age=int(raw_input("How old are you? "))
Is two distinct statements. Either use a line-break (as you did), or insert a semicolon between the two

print "Hi",; age=int(raw_input("How old are you? "))

[pmasiar]

Comma is the tuple constructor operator, so you can ie. assign tuple to tuple:

a, b, c = 1, {'k': 'val'}, 'hi'

where value of b is dictionary, just to make it less boring