Milt,
On 6/03/19 11:39 AM, Milt wrote:
The following code gives me unusual results - base on experience with C++.
class Car:
# carColor = None
# mileage = None
def __init__(self, color = None, miles = None):
self.mileage = miles
self.carColor = color
def print(self):
print(f"Color: {self.carColor}")
print(f"Mileage: {self.mileage}")
myCar = Car('blue', 15000)
myCar.print()
print()
myCar = Car(25000, 'orange')
myCar.print()
When executed the following results:
Color: blue
Mileage: 15000
Color: 25000
Mileage: orange
It appears that the constructor ignores the assignment statements and
makes the assignment based on the ordering in the __init__ declaration.
It is risky to decide that Python should behave in a certain fashion,
just because another language does. Would you decide that the word
"blue" may not be used because in French it is "bleu"? If all
programming languages did look/work the same way, why would there be
multiple languages? However, your understanding of C++ gives you a
flying start with Python - apart from a few pesky 'gotchas'!
In the term "ignores the assignment statements", what "assignment
statements" are being discussed?
Yes, without keywords, the positional rule applies.
myCar = Car('blue', 15000)
is the same as:
myCar = Car(color = 'blue', miles = 15000)
Instead of:
myCar = Car(25000, 'orange')
try:
myCar = Car(miles=25000, color='orange')
If you've gone to the trouble of defining keyword-arguments in the
method, greater satisfaction will be gained from calling the method
similarly (and cause less confusion on the part of your readers!)
Meantime I have a very low-mileage Edsel in an attractive lemon color,
going cheap...
Jokes aside: using the __str__() and __repr__() "magic methods" is more
'pythonic' than adding a print method to a class.
For a nicely-formatted output (albeit without mentioning that it is
describing a "Car" or "myCar" - per print(), above):
def __str__(self):
return f"Color: {self.carColor}\nMileage: {self.mileage}"
...
myCar = Car(color = 'blue', miles = 15000)
print( myCar )
For extra credit, seeing we're talking about 'being pythonic': car_color
and my_car.
Alternately, to present the output formatted as a class definition/ready
for instantiation:
def __repr__(self):
return f"Car( color={self.car_color}, miles={self.mileage} )"
NB if both methods appear in a class, printing the class (ie print(
my_car ) ) will prefer __repr__() over __str__().
All the best...
--
Regards =dn
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