Variables declared inside the class definition, but not inside a method are class or static variables:
>>> class MyClass:
... i = 3
...
>>> MyClass.i
3
As @millerdev points out, this creates a class-level i
variable, but this is distinct from any instance-level i
variable, so you could have
>>> m = MyClass()
>>> m.i = 4
>>> MyClass.i, m.i
>>> (3, 4)
This is different from C++ and Java, but not so different from C#, where a static member can't be accessed using a reference to an instance.
See what the Python tutorial has to say on the subject of classes and class objects.
@Steve Johnson has already answered regarding static methods, also documented under "Built-in Functions" in the Python Library Reference.
class C:
@staticmethod
def f(arg1, arg2, ...): ...
@beidy recommends classmethods over staticmethod, as the method then receives the class type as the first argument, but I'm still a little fuzzy on the advantages of this approach over staticmethod. If you are too, then it probably doesn't matter.
If the reason you're checking is so you can do something like if file_exists: open_it()
, it's safer to use a try
around the attempt to open it. Checking and then opening risks the file being deleted or moved or something between when you check and when you try to open it.
If you're not planning to open the file immediately, you can use os.path.isfile
Return True
if path is an existing regular file. This follows symbolic links, so both islink() and isfile() can be true for the same path.
import os.path
os.path.isfile(fname)
if you need to be sure it's a file.
Starting with Python 3.4, the pathlib
module offers an object-oriented approach (backported to pathlib2
in Python 2.7):
from pathlib import Path
my_file = Path("/path/to/file")
if my_file.is_file():
# file exists
To check a directory, do:
if my_file.is_dir():
# directory exists
To check whether a Path
object exists independently of whether is it a file or directory, use exists()
:
if my_file.exists():
# path exists
You can also use resolve(strict=True)
in a try
block:
try:
my_abs_path = my_file.resolve(strict=True)
except FileNotFoundError:
# doesn't exist
else:
# exists
Best Answer
Use just the
.getter
decorator of the original property:Note that you have to use the full name to reach the original property descriptor on the parent class.
Demonstration:
The
property
descriptor object is just one object, even though it can have multiple methods associated with it (the getter, setter and deleter). The.getter
,.setter
and.deleter
decorator functions provided by an existingproperty
descriptor return a copy of the descriptor itself, with that one specific method replaced.So in your
human
base class what happens is that you first create the descriptor with the@property
decorator, then replace that descriptor with one that has both a getter and a setter with the@name.setter
syntax. That works because python decorators replace the original decorated function with the same name, it basically executesname = name.setter(name)
. See How does the @property decorator work? for the details on how that all works.In your subclass you simply use that trick to create a new copy of the descriptor with just the getter replaced.