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Python memoising/deferred lookup property decorator
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from boltons.cacheutils import cachedproperty
class Foo(object):
def __init__(self):
self.value = 4
@cachedproperty
def cached_prop(self):
self.value += 1
return self.value
f = Foo()
print(f.value) # initial value
print(f.cached_prop) # cached property is c...
How to implement a good __hash__ function in python [duplicate]
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__hash__ should return the same value for objects that are equal. It also shouldn't change over the lifetime of the object; generally you only implement it for immutable objects.
A trivial implementation would be to just ret...
Convert a python 'type' object to a string
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print type(someObject).__name__
If that doesn't suit you, use this:
print some_instance.__class__.__name__
Example:
class A:
pass
print type(A())
# prints <type 'instance'>
print A().__class__.__name__
# prints A
Also, it seems th...
How to get a function name as a string?
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my_function.__name__
Using __name__ is the preferred method as it applies uniformly. Unlike func_name, it works on built-in functions as well:
>>> import time
>>> time.time.func_name
Traceback (most recent ...
Underscore vs Double underscore with variables and methods [duplicate]
Somebody was nice enough to explain to me that __method() mangles but instead of bothering him further since there are a lot of other people who need help I was wondering if somebody could elaborate the differences further.
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How to decorate a class?
...r specific scenario, YMMV :-)
What you're thinking of is a metaclass. The __new__ function in a metaclass is passed the full proposed definition of the class, which it can then rewrite before the class is created. You can, at that time, sub out the constructor for a new one.
Example:
def substitu...
What is the purpose of the -m switch?
...s this only works on the subset of modules that are executable i.e. have a __main__.py file. Most don't and will break e.g. python -m sys 'print(sys.version)' fails with python: No code object available for sys. Suggest you make that clear in the answer.
– smci
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Inheritance and Overriding __init__ in python
...his nowadays:
class FileInfo(dict):
"""store file metadata"""
def __init__(self, filename=None):
super(FileInfo, self).__init__()
self["name"] = filename
Note the following:
We can directly subclass built-in classes, like dict, list, tuple, etc.
The super function handle...
How to add property to a class dynamically?
...ibute, on a given class. Kinda like a way to factor a huge if tree out of __getattribute__.
When I ask for foo.b in the example above, Python sees that the b defined on the class implements the descriptor protocol—which just means it's an object with a __get__, __set__, or __delete__ method. Th...
RuntimeError on windows trying python multiprocessing
...l import (i.e. execute) the main module at start. You need to insert an if __name__ == '__main__': guard in the main module to avoid creating subprocesses recursively.
Modified testMain.py:
import parallelTestModule
if __name__ == '__main__':
extractor = parallelTestModule.ParallelExtrac...