I cannot initialize class in python

Question

I have a class Flight, and I'm trying initialize it, but I have a syntax error in

print x=Flight(flightFromInput='nebrasca')

This is a content of my example file

class Flight:
    flightFrom = None
    flightTo = None
    departureDate = None
    arrivalDate=None
    airline=None
    serviceClass=None
    departureAirport = None
    arrivalAirport=None


    #----------------------------------------------------------------------
    def __init__(self,flightFromInput):
        self.flightFrom = flightFromInput

print x=Flight(flightFromInput='nebrasca')

What is wrong with this code?

Also: Do you realize that variables created in class scope (in your code, every assignment above #-----...) are class variables, i.e. shared among instances, and not instance variables (self....)? — user395760
– user395760, Commented Jan 26, 2011 at 14:45
@delnan: The class variables can act as fall-backs. If you assign to .flightFrom on an instance, you won't change the class variable, so semantically this is ok. (You might have objections regarding the style, though.) — Sven Marnach
– Sven Marnach, Commented Jan 26, 2011 at 14:47
@Sven: That why I asked "do you realize" instead of writng "your code is propably broken". But yes, I do wonder if this is the best solution. — user395760
– user395760, Commented Jan 26, 2011 at 14:50
@S.Lott: It's not entirely unreasonable to expect assignment to be an expression (there are many popular languages that do this). Especially given that OP seems to know some of those (e.g. asked C# questions). — user395760
– user395760, Commented Jan 26, 2011 at 14:55

Don · Accepted Answer · 2011-01-26 14:43:42Z

8

You should write

x = Flight(flightFromInput='nebrasca')
print x

answered Jan 26, 2011 at 14:43

Don

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Comments

Frank · Accepted Answer · 2011-01-26 14:46:23Z

4

In python an assignment statement doesn't return the assigned value. So you cannot use it within another statement. As the other answers suggested, you can work around this by printing x in a separate line.

Note, that there are exceptions though:

a = b = 0 # works
a = (b = 0) # does not work

The first case is a special case allowed for convenience when you want to assign the same value to multiple variables. In the second case you clearly tell the compiler that b=0 is a separate statement, but as it doesn't return a value the outer assignment to a leads to the resulting SyntaxError.

Hope this explains it a bit more clearly, why you should do print x after assigning it.

answered Jan 26, 2011 at 14:46

Frank

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Comments

thkala · Accepted Answer · 2011-01-26 14:45:49Z

1

Contrary to C, in Python assignments are statements only and not expressions. Therefore they do not have their own value. Try this:

x = Flight(flightFromInput='nebrasca')
print x

answered Jan 26, 2011 at 14:45

thkala

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