Let's say we have a function foo()
def foo():
foo.a = 2
foo.a = 1
foo()
>> foo.a
>> 2
Is this pythonic or should I wrap the variable in mutable objects such as a list?
Eg:
a = [1]
def foo(a):
a[0] = 2
foo()
>> a
>> 2
2 Answers
Since you "want to mutate the variable so that the changes are effected in global scope as well" use the global keyword to tell your function that the name a is a global variable. This means that any assignment to a inside of your function affects the global scope. Without the global declaration assignment to a in your function would create a new local variable.
>>> a = 0
>>> def foo():
... global a
... a = 1
...
>>> foo()
>>> a
1
answered Oct 18, 2016 at 14:29
4 Comments
yask
Can you also explain what
foo.a means where foo is a function name. How does the example 1 (as mentioned in the question) work like a mutable variable?Steven Rumbalski
@yask: Python functions are callable objects. Since they are objects you can add attributes using dot notation (such as
foo.a = 2). This is a legal but not common practice (but not totally uncommon). If you need to pair behavior with state what you want is to declare a class.
jbndlr
@StevenRumbalski
a is no attribute in your example, this may be misleading.Steven Rumbalski
@jbndlr: I'm addressing yask's goal as stated in his comment to the question.
Use a class (maybe a bit overkill):
class Foo:
def __init__(self):
self.a = 0
def bar(f):
f.a = 2
foo = Foo()
foo.a = 1
bar(foo)
print(foo.a)
1 Comment
bruno desthuilliers
I assume you meant
self.a = 0 in Foo.__init__ ?
function_name.a(Eg 1) means and why does it simulate mutable object?globalkeywords).