How to avoid creating a class attribute by accident












1















I know the motto is "we're all consenting adults around here."



but here is a problem I spent a day on. I got passed a class with over 100 attributes. I had specified one of them was to be called "run_count". The front-end had a place to enter run_count.



Somehow, the front-end/back-end package people decided to call it "run_iterations" instead.



So, my problem is I am writing unit test software, and I did this:



passed_parameters.run_count = 100
result = do_the_thing(passed_parameters)
assert result == 99.75


Now, the problem, of course, is that Python willingly let me set this "new" attribute called "run_count". But, after delving 10 levels down into the code, I discover that the function "do_the_thing" (obviously) never looks at "run_count", but uses "passed_paramaters.run_iterations" instead.



Is there some simple way to avoid allowing yourself to create a new attribute in a class, or a new entry in a dictionary, when you naievely assume you know the attribute name (or the dict key), and accidentally create a new entry that never gets looked at?



In an ideal world, no matter how dynamic, Python would allow you to "lock" and object or instance of one. Then, trying to set a new value for an attribute that doesn't exist would raise an attribute error, letting you know you are trying to change something that doesn't exist, rather than letting you create a new attribute that never gets used.










share|improve this question


















  • 1





    It seems you are looking for an statically typed language

    – Josué Cortina
    Dec 29 '18 at 6:28











  • No, just looking for a way to avoid wasted time on complex projects. As I noted, most of the dat went into tracking down what attribute - other than the one I had asked for - got specified on the front-end and used deep in the back-end, where it was not what I expected. This is a nightmare for large projects: suppose you develop a class, someone redefines an attribute or method for it that changes it but their code relies on it, but that def changes later. It would be a nightmare to track down that what got lost was someone's redefinition you never knew of.

    – eSurfsnake
    Dec 29 '18 at 6:31
















1















I know the motto is "we're all consenting adults around here."



but here is a problem I spent a day on. I got passed a class with over 100 attributes. I had specified one of them was to be called "run_count". The front-end had a place to enter run_count.



Somehow, the front-end/back-end package people decided to call it "run_iterations" instead.



So, my problem is I am writing unit test software, and I did this:



passed_parameters.run_count = 100
result = do_the_thing(passed_parameters)
assert result == 99.75


Now, the problem, of course, is that Python willingly let me set this "new" attribute called "run_count". But, after delving 10 levels down into the code, I discover that the function "do_the_thing" (obviously) never looks at "run_count", but uses "passed_paramaters.run_iterations" instead.



Is there some simple way to avoid allowing yourself to create a new attribute in a class, or a new entry in a dictionary, when you naievely assume you know the attribute name (or the dict key), and accidentally create a new entry that never gets looked at?



In an ideal world, no matter how dynamic, Python would allow you to "lock" and object or instance of one. Then, trying to set a new value for an attribute that doesn't exist would raise an attribute error, letting you know you are trying to change something that doesn't exist, rather than letting you create a new attribute that never gets used.










share|improve this question


















  • 1





    It seems you are looking for an statically typed language

    – Josué Cortina
    Dec 29 '18 at 6:28











  • No, just looking for a way to avoid wasted time on complex projects. As I noted, most of the dat went into tracking down what attribute - other than the one I had asked for - got specified on the front-end and used deep in the back-end, where it was not what I expected. This is a nightmare for large projects: suppose you develop a class, someone redefines an attribute or method for it that changes it but their code relies on it, but that def changes later. It would be a nightmare to track down that what got lost was someone's redefinition you never knew of.

    – eSurfsnake
    Dec 29 '18 at 6:31














1












1








1


1






I know the motto is "we're all consenting adults around here."



but here is a problem I spent a day on. I got passed a class with over 100 attributes. I had specified one of them was to be called "run_count". The front-end had a place to enter run_count.



Somehow, the front-end/back-end package people decided to call it "run_iterations" instead.



So, my problem is I am writing unit test software, and I did this:



passed_parameters.run_count = 100
result = do_the_thing(passed_parameters)
assert result == 99.75


Now, the problem, of course, is that Python willingly let me set this "new" attribute called "run_count". But, after delving 10 levels down into the code, I discover that the function "do_the_thing" (obviously) never looks at "run_count", but uses "passed_paramaters.run_iterations" instead.



Is there some simple way to avoid allowing yourself to create a new attribute in a class, or a new entry in a dictionary, when you naievely assume you know the attribute name (or the dict key), and accidentally create a new entry that never gets looked at?



In an ideal world, no matter how dynamic, Python would allow you to "lock" and object or instance of one. Then, trying to set a new value for an attribute that doesn't exist would raise an attribute error, letting you know you are trying to change something that doesn't exist, rather than letting you create a new attribute that never gets used.










share|improve this question














I know the motto is "we're all consenting adults around here."



but here is a problem I spent a day on. I got passed a class with over 100 attributes. I had specified one of them was to be called "run_count". The front-end had a place to enter run_count.



Somehow, the front-end/back-end package people decided to call it "run_iterations" instead.



So, my problem is I am writing unit test software, and I did this:



passed_parameters.run_count = 100
result = do_the_thing(passed_parameters)
assert result == 99.75


Now, the problem, of course, is that Python willingly let me set this "new" attribute called "run_count". But, after delving 10 levels down into the code, I discover that the function "do_the_thing" (obviously) never looks at "run_count", but uses "passed_paramaters.run_iterations" instead.



Is there some simple way to avoid allowing yourself to create a new attribute in a class, or a new entry in a dictionary, when you naievely assume you know the attribute name (or the dict key), and accidentally create a new entry that never gets looked at?



In an ideal world, no matter how dynamic, Python would allow you to "lock" and object or instance of one. Then, trying to set a new value for an attribute that doesn't exist would raise an attribute error, letting you know you are trying to change something that doesn't exist, rather than letting you create a new attribute that never gets used.







python-3.x






share|improve this question













share|improve this question











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share|improve this question










asked Dec 29 '18 at 6:21









eSurfsnakeeSurfsnake

279110




279110








  • 1





    It seems you are looking for an statically typed language

    – Josué Cortina
    Dec 29 '18 at 6:28











  • No, just looking for a way to avoid wasted time on complex projects. As I noted, most of the dat went into tracking down what attribute - other than the one I had asked for - got specified on the front-end and used deep in the back-end, where it was not what I expected. This is a nightmare for large projects: suppose you develop a class, someone redefines an attribute or method for it that changes it but their code relies on it, but that def changes later. It would be a nightmare to track down that what got lost was someone's redefinition you never knew of.

    – eSurfsnake
    Dec 29 '18 at 6:31














  • 1





    It seems you are looking for an statically typed language

    – Josué Cortina
    Dec 29 '18 at 6:28











  • No, just looking for a way to avoid wasted time on complex projects. As I noted, most of the dat went into tracking down what attribute - other than the one I had asked for - got specified on the front-end and used deep in the back-end, where it was not what I expected. This is a nightmare for large projects: suppose you develop a class, someone redefines an attribute or method for it that changes it but their code relies on it, but that def changes later. It would be a nightmare to track down that what got lost was someone's redefinition you never knew of.

    – eSurfsnake
    Dec 29 '18 at 6:31








1




1





It seems you are looking for an statically typed language

– Josué Cortina
Dec 29 '18 at 6:28





It seems you are looking for an statically typed language

– Josué Cortina
Dec 29 '18 at 6:28













No, just looking for a way to avoid wasted time on complex projects. As I noted, most of the dat went into tracking down what attribute - other than the one I had asked for - got specified on the front-end and used deep in the back-end, where it was not what I expected. This is a nightmare for large projects: suppose you develop a class, someone redefines an attribute or method for it that changes it but their code relies on it, but that def changes later. It would be a nightmare to track down that what got lost was someone's redefinition you never knew of.

– eSurfsnake
Dec 29 '18 at 6:31





No, just looking for a way to avoid wasted time on complex projects. As I noted, most of the dat went into tracking down what attribute - other than the one I had asked for - got specified on the front-end and used deep in the back-end, where it was not what I expected. This is a nightmare for large projects: suppose you develop a class, someone redefines an attribute or method for it that changes it but their code relies on it, but that def changes later. It would be a nightmare to track down that what got lost was someone's redefinition you never knew of.

– eSurfsnake
Dec 29 '18 at 6:31












1 Answer
1






active

oldest

votes


















4














Use __setattr__, and check the attribute exists, otherwise, throw an error. If you do this, you will receive an error when you define those attributes inside __init__, so you have to workaround that situation. I found 4 ways of doing that. First, define those attributes inside the class, that way, when you try to set their initial value they will already be defined. Second, call object.__setattr__ directly. Third, add a fourth boolean param to __setattr__ indicating whether to bypass checking or not. Fourth, define the previous boolean flag as class-wide, set it to True, initialize the fields and set the flag back to False. Here is the code:



Code



class A:
f = 90
a = None

bypass_check = False

def __init__(self, a, b, c, d1, d2, d3, d4):
# 1st workaround
self.a = a

# 2nd workaround
object.__setattr__(self, 'b', b)

# 3rd workaround
self.__setattr__('c', c, True)

# 4th workaround
self.bypass_check = True
self.d1 = d1
self.d2 = d2
self.d3 = d3
self.d4 = d4
self.bypass_check = False

def __setattr__(self, attr, value, bypass=False):
if bypass or self.bypass_check or hasattr(self, attr):
object.__setattr__(self, attr, value)
else:
# Throw some error
print('Attribute %s not found' % attr)

a = A(1, 2, 3, 4, 5, 6, 7)
a.f = 100
a.d1 = -1
a.g = 200
print(a.f, a.a, a.d1, a.d4)


Output



Attribute g not found
100 1 -1 7





share|improve this answer


























  • In the right area, but how to avoid accidentally creating new attributes, not calling for ones that don't exiist?

    – eSurfsnake
    Dec 29 '18 at 6:39











  • It seems there ought to be a __setattr__(), and one could put a hook in there. Something like: def __set_attr__(attr, value): if not __get_attr__(attr) raise <proper error> else <go and__setattr__()>

    – eSurfsnake
    Dec 29 '18 at 6:40













  • eSurfsnake, I edited the code... that should work

    – Josué Cortina
    Dec 29 '18 at 6:49











  • yes, exactly what I was looking for. Thanks!.

    – eSurfsnake
    Dec 29 '18 at 6:50











  • @eSurfsnake please, remember to mark my answer as accepted (green checkmark) and up vote it if this worked for you. Thanks in advance!

    – Josué Cortina
    Dec 29 '18 at 17:02











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1 Answer
1






active

oldest

votes








1 Answer
1






active

oldest

votes









active

oldest

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active

oldest

votes









4














Use __setattr__, and check the attribute exists, otherwise, throw an error. If you do this, you will receive an error when you define those attributes inside __init__, so you have to workaround that situation. I found 4 ways of doing that. First, define those attributes inside the class, that way, when you try to set their initial value they will already be defined. Second, call object.__setattr__ directly. Third, add a fourth boolean param to __setattr__ indicating whether to bypass checking or not. Fourth, define the previous boolean flag as class-wide, set it to True, initialize the fields and set the flag back to False. Here is the code:



Code



class A:
f = 90
a = None

bypass_check = False

def __init__(self, a, b, c, d1, d2, d3, d4):
# 1st workaround
self.a = a

# 2nd workaround
object.__setattr__(self, 'b', b)

# 3rd workaround
self.__setattr__('c', c, True)

# 4th workaround
self.bypass_check = True
self.d1 = d1
self.d2 = d2
self.d3 = d3
self.d4 = d4
self.bypass_check = False

def __setattr__(self, attr, value, bypass=False):
if bypass or self.bypass_check or hasattr(self, attr):
object.__setattr__(self, attr, value)
else:
# Throw some error
print('Attribute %s not found' % attr)

a = A(1, 2, 3, 4, 5, 6, 7)
a.f = 100
a.d1 = -1
a.g = 200
print(a.f, a.a, a.d1, a.d4)


Output



Attribute g not found
100 1 -1 7





share|improve this answer


























  • In the right area, but how to avoid accidentally creating new attributes, not calling for ones that don't exiist?

    – eSurfsnake
    Dec 29 '18 at 6:39











  • It seems there ought to be a __setattr__(), and one could put a hook in there. Something like: def __set_attr__(attr, value): if not __get_attr__(attr) raise <proper error> else <go and__setattr__()>

    – eSurfsnake
    Dec 29 '18 at 6:40













  • eSurfsnake, I edited the code... that should work

    – Josué Cortina
    Dec 29 '18 at 6:49











  • yes, exactly what I was looking for. Thanks!.

    – eSurfsnake
    Dec 29 '18 at 6:50











  • @eSurfsnake please, remember to mark my answer as accepted (green checkmark) and up vote it if this worked for you. Thanks in advance!

    – Josué Cortina
    Dec 29 '18 at 17:02
















4














Use __setattr__, and check the attribute exists, otherwise, throw an error. If you do this, you will receive an error when you define those attributes inside __init__, so you have to workaround that situation. I found 4 ways of doing that. First, define those attributes inside the class, that way, when you try to set their initial value they will already be defined. Second, call object.__setattr__ directly. Third, add a fourth boolean param to __setattr__ indicating whether to bypass checking or not. Fourth, define the previous boolean flag as class-wide, set it to True, initialize the fields and set the flag back to False. Here is the code:



Code



class A:
f = 90
a = None

bypass_check = False

def __init__(self, a, b, c, d1, d2, d3, d4):
# 1st workaround
self.a = a

# 2nd workaround
object.__setattr__(self, 'b', b)

# 3rd workaround
self.__setattr__('c', c, True)

# 4th workaround
self.bypass_check = True
self.d1 = d1
self.d2 = d2
self.d3 = d3
self.d4 = d4
self.bypass_check = False

def __setattr__(self, attr, value, bypass=False):
if bypass or self.bypass_check or hasattr(self, attr):
object.__setattr__(self, attr, value)
else:
# Throw some error
print('Attribute %s not found' % attr)

a = A(1, 2, 3, 4, 5, 6, 7)
a.f = 100
a.d1 = -1
a.g = 200
print(a.f, a.a, a.d1, a.d4)


Output



Attribute g not found
100 1 -1 7





share|improve this answer


























  • In the right area, but how to avoid accidentally creating new attributes, not calling for ones that don't exiist?

    – eSurfsnake
    Dec 29 '18 at 6:39











  • It seems there ought to be a __setattr__(), and one could put a hook in there. Something like: def __set_attr__(attr, value): if not __get_attr__(attr) raise <proper error> else <go and__setattr__()>

    – eSurfsnake
    Dec 29 '18 at 6:40













  • eSurfsnake, I edited the code... that should work

    – Josué Cortina
    Dec 29 '18 at 6:49











  • yes, exactly what I was looking for. Thanks!.

    – eSurfsnake
    Dec 29 '18 at 6:50











  • @eSurfsnake please, remember to mark my answer as accepted (green checkmark) and up vote it if this worked for you. Thanks in advance!

    – Josué Cortina
    Dec 29 '18 at 17:02














4












4








4







Use __setattr__, and check the attribute exists, otherwise, throw an error. If you do this, you will receive an error when you define those attributes inside __init__, so you have to workaround that situation. I found 4 ways of doing that. First, define those attributes inside the class, that way, when you try to set their initial value they will already be defined. Second, call object.__setattr__ directly. Third, add a fourth boolean param to __setattr__ indicating whether to bypass checking or not. Fourth, define the previous boolean flag as class-wide, set it to True, initialize the fields and set the flag back to False. Here is the code:



Code



class A:
f = 90
a = None

bypass_check = False

def __init__(self, a, b, c, d1, d2, d3, d4):
# 1st workaround
self.a = a

# 2nd workaround
object.__setattr__(self, 'b', b)

# 3rd workaround
self.__setattr__('c', c, True)

# 4th workaround
self.bypass_check = True
self.d1 = d1
self.d2 = d2
self.d3 = d3
self.d4 = d4
self.bypass_check = False

def __setattr__(self, attr, value, bypass=False):
if bypass or self.bypass_check or hasattr(self, attr):
object.__setattr__(self, attr, value)
else:
# Throw some error
print('Attribute %s not found' % attr)

a = A(1, 2, 3, 4, 5, 6, 7)
a.f = 100
a.d1 = -1
a.g = 200
print(a.f, a.a, a.d1, a.d4)


Output



Attribute g not found
100 1 -1 7





share|improve this answer















Use __setattr__, and check the attribute exists, otherwise, throw an error. If you do this, you will receive an error when you define those attributes inside __init__, so you have to workaround that situation. I found 4 ways of doing that. First, define those attributes inside the class, that way, when you try to set their initial value they will already be defined. Second, call object.__setattr__ directly. Third, add a fourth boolean param to __setattr__ indicating whether to bypass checking or not. Fourth, define the previous boolean flag as class-wide, set it to True, initialize the fields and set the flag back to False. Here is the code:



Code



class A:
f = 90
a = None

bypass_check = False

def __init__(self, a, b, c, d1, d2, d3, d4):
# 1st workaround
self.a = a

# 2nd workaround
object.__setattr__(self, 'b', b)

# 3rd workaround
self.__setattr__('c', c, True)

# 4th workaround
self.bypass_check = True
self.d1 = d1
self.d2 = d2
self.d3 = d3
self.d4 = d4
self.bypass_check = False

def __setattr__(self, attr, value, bypass=False):
if bypass or self.bypass_check or hasattr(self, attr):
object.__setattr__(self, attr, value)
else:
# Throw some error
print('Attribute %s not found' % attr)

a = A(1, 2, 3, 4, 5, 6, 7)
a.f = 100
a.d1 = -1
a.g = 200
print(a.f, a.a, a.d1, a.d4)


Output



Attribute g not found
100 1 -1 7






share|improve this answer














share|improve this answer



share|improve this answer








edited Dec 30 '18 at 20:03

























answered Dec 29 '18 at 6:36









Josué CortinaJosué Cortina

1,286212




1,286212













  • In the right area, but how to avoid accidentally creating new attributes, not calling for ones that don't exiist?

    – eSurfsnake
    Dec 29 '18 at 6:39











  • It seems there ought to be a __setattr__(), and one could put a hook in there. Something like: def __set_attr__(attr, value): if not __get_attr__(attr) raise <proper error> else <go and__setattr__()>

    – eSurfsnake
    Dec 29 '18 at 6:40













  • eSurfsnake, I edited the code... that should work

    – Josué Cortina
    Dec 29 '18 at 6:49











  • yes, exactly what I was looking for. Thanks!.

    – eSurfsnake
    Dec 29 '18 at 6:50











  • @eSurfsnake please, remember to mark my answer as accepted (green checkmark) and up vote it if this worked for you. Thanks in advance!

    – Josué Cortina
    Dec 29 '18 at 17:02



















  • In the right area, but how to avoid accidentally creating new attributes, not calling for ones that don't exiist?

    – eSurfsnake
    Dec 29 '18 at 6:39











  • It seems there ought to be a __setattr__(), and one could put a hook in there. Something like: def __set_attr__(attr, value): if not __get_attr__(attr) raise <proper error> else <go and__setattr__()>

    – eSurfsnake
    Dec 29 '18 at 6:40













  • eSurfsnake, I edited the code... that should work

    – Josué Cortina
    Dec 29 '18 at 6:49











  • yes, exactly what I was looking for. Thanks!.

    – eSurfsnake
    Dec 29 '18 at 6:50











  • @eSurfsnake please, remember to mark my answer as accepted (green checkmark) and up vote it if this worked for you. Thanks in advance!

    – Josué Cortina
    Dec 29 '18 at 17:02

















In the right area, but how to avoid accidentally creating new attributes, not calling for ones that don't exiist?

– eSurfsnake
Dec 29 '18 at 6:39





In the right area, but how to avoid accidentally creating new attributes, not calling for ones that don't exiist?

– eSurfsnake
Dec 29 '18 at 6:39













It seems there ought to be a __setattr__(), and one could put a hook in there. Something like: def __set_attr__(attr, value): if not __get_attr__(attr) raise <proper error> else <go and__setattr__()>

– eSurfsnake
Dec 29 '18 at 6:40







It seems there ought to be a __setattr__(), and one could put a hook in there. Something like: def __set_attr__(attr, value): if not __get_attr__(attr) raise <proper error> else <go and__setattr__()>

– eSurfsnake
Dec 29 '18 at 6:40















eSurfsnake, I edited the code... that should work

– Josué Cortina
Dec 29 '18 at 6:49





eSurfsnake, I edited the code... that should work

– Josué Cortina
Dec 29 '18 at 6:49













yes, exactly what I was looking for. Thanks!.

– eSurfsnake
Dec 29 '18 at 6:50





yes, exactly what I was looking for. Thanks!.

– eSurfsnake
Dec 29 '18 at 6:50













@eSurfsnake please, remember to mark my answer as accepted (green checkmark) and up vote it if this worked for you. Thanks in advance!

– Josué Cortina
Dec 29 '18 at 17:02





@eSurfsnake please, remember to mark my answer as accepted (green checkmark) and up vote it if this worked for you. Thanks in advance!

– Josué Cortina
Dec 29 '18 at 17:02


















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