Questions tagged [hasattr]
38 questions
97
votes
13 answers
hasattr() vs try-except block to deal with non-existent attributes
if hasattr(obj, 'attribute'):
# do somthing
vs
try:
# access obj.attribute
except AttributeError, e:
# deal with AttributeError
Which should be preferred and why?
Imran
- 87,203
- 23
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- 131
39
votes
6 answers
Python's hasattr on list values of dictionaries always returns false?
I have a dictionary that sometimes receives calls for non-existent keys, so I try and use hasattr and getattr to handle these cases:
key_string = 'foo'
print "current info:", info
print hasattr(info, key_string)
print getattr(info, key_string,…
Chris Keele
- 3,364
- 3
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- 52
27
votes
5 answers
Checking for member existence in Python
I regularly want to check if an object has a member or not. An example is the creation of a singleton in a function. For that purpose, you can use hasattr like this:
class Foo(object):
@classmethod
def singleton(self):
if not…
PierreBdR
- 42,120
- 10
- 46
- 62
9
votes
2 answers
How to prevent hasattr from retrieving the attribute value itself
I have a class that implements virtual attributes using __getattr__. The attributes can be expensive, e.g. performing a query. Now, I am using a library which checks if my object has the attribute before actually getting it.
As a consequence, a…
koriander
- 3,110
- 2
- 15
- 23
6
votes
1 answer
Python's hasattr sometimes returns incorrect results
Why does hasattr say that the instance doesn't have a foo attribute?
>>> class A(object):
... @property
... def foo(self):
... ErrorErrorError
...
>>> a = A()
>>> hasattr(a, 'foo')
False
I expected:
>>> hasattr(a, 'foo')
NameError:…
wim
- 338,267
- 99
- 616
- 750
5
votes
2 answers
How to robustly check a Python property exists?
Given the following class (with a buggy property) then what is the best foolproof way of checking that the bar property exists?
class Foo(object):
@property
def bar(self):
raise AttributeError('unforeseen attribute error!')
Both…
101
- 8,514
- 6
- 43
- 69
5
votes
3 answers
hasattr on class names
hasattr documentation says that it takes an object and an attribute name and lets you know if that attribute exists on that object.
I have discovered that it seems to work on class names too (i.e. not an instance object).
Something like:
class A:
…
Programmer Person
- 598
- 3
- 12
5
votes
6 answers
Check multiples hasattr in the same condition
if hasattr(form, 'name') and hasattr(form, 'date'):
print(form.name) #'Some name' - True
print(form.date) #none - False
This condition validates as True even if the hasattr(form, 'date') is false.
What is the correct way to validate multiples…
user2983258
- 151
- 1
- 3
- 9
3
votes
2 answers
How to test if python class parent has method defined?
I have a subclass that may have a method 'method_x' defined. I want to know if 'method_x' was defined somewhere else up the class hierarchy.
If I do:
hasattr(self, 'method_x')
I'll get a truth value that also looks at any methods defined for the…
piRSquared
- 285,575
- 57
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3
votes
2 answers
hasattr keeps returning False
class Avatar:
def __init__(self, HP=100, damage=10, defends=10, magic=5):
self.__hp = HP
self.__dam = damage
self.__def = defends
self.__mag = magic
def check_hasattr(self):
print…
anonymous_1123581321
- 31
- 3
3
votes
2 answers
Is there a function in python that returns true if all members of an iterable are true?
I'm tryng to learn different ways to do simple things in python, while also learning a bit about some functional practices. I have some numbers that the user inputs, and I want to know if they really are numbers. I've come up with this kind of…
ferhtgoldaraz
- 1,693
- 3
- 15
- 20
2
votes
2 answers
How detect hashable types with structural pattern matching?
Using structural pattern matching, how do you write a case that matches instances of hashable types?
I've tried:
for obj in [], (), set(), frozenset(), 10, None, dict():
match obj:
case object(__hash__=_):
print('Hashable…
Raymond Hettinger
- 216,523
- 63
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- 485
2
votes
2 answers
How to filter an array of objects on nested attribute using lambda and hasattr?
I have the following Python code:
myArray = [{ "id": 1, "desc": "foo", "specs": { "width": 1, "height": 1}}, { "id": 2, "desc": "bar", "specs": { "width": 2, "height": 2, "color": "black"}}, { "id": 3, "desc": "foobar"}]
print…
smartmouse
- 13,912
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2
votes
1 answer
Python 3 - Check class attribute without calling __getattr__
TL;DR: Are there alternatives to hasattr which don't trigger property getters?
I'm writing a Python interface to some existing code where I am getting and setting values for various shape and section classes. Due to a large number of possible…
Tim Jim
- 620
- 5
- 19
2
votes
2 answers
Detect if a __getattribute__ call was due to hasattr
I'm re-implementing __getattribute__ for a class.
I want to notice any incorrect (meaning failures are expected, of course) failures of providing attributes (because the __getattribute__ implementation turned out quite complex). For that I log a…
NirIzr
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