Oregon Curriculum Network
Discovering Math with Python
In [1]:
from keyword import kwlist
print(", ".join(kwlist))
In [2]:
exceptions, callables, not_callables = [], [], []
for name in dir(__builtins__): # cycle through a bunch of strings
obj = eval(name) # turn strings back into objects
if type(obj) == type and issubclass(obj, BaseException):
exceptions.append(name) # types of exception
elif callable(obj):
callables.append(name) # callable
else:
not_callables.append(name) # whatever is left over
print("Exceptions\n", exceptions)
print("------")
print("Callables\n", callables)
print("------")
print("Other\n", not_callables)
Special names all have a similar look: __name__
In other words: two underlines, a name, two underlines. I sometimes think of the special names as the Python's __ribs__ (snakes have lots of ribs).
You don't make up or define these special names yourself. They come with the language. Newer versions of Python may have more of them, but within a given version, they're fixed.
Think of special names as like the strings a puppeteer uses to control marrionettes. Each string goes to a specific aspect of Python's grammar, such as calling an object, getting or setting an object's attribute, getting or setting using index notation (square brackets).
Many object types come with predefined behaviors for any or all of the above. When you write your own classes, or subclass an existing type, that's when you have the ability to define or override some special name behavior.
In [3]:
"""
This type of object gets along with nobody!
or·ner·y
ˈôrn(ə)rē/
adjective North American informal
adjective: ornery
bad-tempered and combative.
"some hogs are just mean and ornery"
synonyms: grouchy, grumpy, cranky, crotchety, cantankerous, bad-tempered,
ill-tempered, dyspeptic, irascible, waspish
自 = self in Chinese (showing that self is not a keyword, just a placeholder)
"""
class Ornery:
def __init__(自, name="Fred"):
自.name = name
print("A sourpuss is born!")
def __getitem__(自, key):
return "How dare you touch me with those brackets!"
def __call__(自, *args, **kwargs):
return "Don't call me at home!"
def __getattr__(自, attr):
return "I'm insulted you'd suppose I'd have {}".format(attr)
def __repr__(自):
return "Don't bother me! Go away."
def __invert__(自):
return "I can't invert, are you kidding?"
grumpy = Ornery()
print(grumpy("Hello?")) # __call__
print(grumpy.mood) # __getattr__
print(grumpy[3]) # __getitem__
print(~grumpy) # __invert__
print(grumpy) # __repr__