update: Just saw the reference to call_user_func_array
in your post. that's different. use getattr
to get the function object and then call it with your arguments
class A[object]:
def method1[self, a, b, c]:
# foo
method = A.method1
method
is now an actual function object. that you can call directly [functions are first class objects in python just like in PHP > 5.3] . But the considerations from below still apply. That is, the above example will blow up unless you decorate A.method1
with one of the two decorators discussed below,
pass it an instance of A
as the first argument or access the method on an instance of A
.
a = A[]
method = a.method1
method[1, 2]
You have three options for doing this
- Use an instance of
A
to callmethod1
[using two possible forms] - apply the
classmethod
decorator tomethod1
: you will no longer be able to referenceself
inmethod1
but you will get passed acls
instance in it's place which isA
in this case. - apply the
staticmethod
decorator tomethod1
: you will no longer be able to referenceself
, orcls
instaticmethod1
but you can hardcode references toA
into it, though obviously, these references will be inherited by all subclasses ofA
unless they specifically overridemethod1
and do not callsuper
.
Some examples:
class Test1[object]: # always inherit from object in 2.x. it's called new-style classes. look it up
def method1[self, a, b]:
return a + b
@staticmethod
def method2[a, b]:
return a + b
@classmethod
def method3[cls, a, b]:
return cls.method2[a, b]
t = Test1[] # same as doing it in another class
Test1.method1[t, 1, 2] #form one of calling a method on an instance
t.method1[1, 2] # form two [the common one] essentially reduces to form one
Test1.method2[1, 2] #the static method can be called with just arguments
t.method2[1, 2] # on an instance or the class
Test1.method3[1, 2] # ditto for the class method. It will have access to the class
t.method3[1, 2] # that it's called on [the subclass if called on a subclass]
# but will not have access to the instance it's called on
# [if it is called on an instance]
Note that in the same way that the name of the self
variable is entirely up to you, so is the name of the cls
variable but those are the customary values.
Now that you know how to do it, I would seriously think about if you want to do it. Often times, methods that are meant to be called unbound [without an instance] are better left as module level functions in python.
View Discussion
Improve Article
Save Article
View Discussion
Improve Article
Save Article
Prerequisite: Functions in Python
In Python,
any written function can be called by another function. Note that this could be the most elegant way of breaking a problem into chunks of small problems. In this article, we will learn how can we call a defined function from another function with help of multiple examples.
Calling and Called Function ?
The Function which calls another Function is called Calling Function and function which is called by another Function is call
Called Function.
How does Function execution work?
A stack data structure is used during the execution of the function calls. Whenever a function is invoked then the calling function is pushed into the stack and called function is executed. When the called function completes its execution and returns then the calling function is popped from the stack and executed. Calling Function execution will be completed only when called Function is execution
completes.
In the below figure. The function call is made from the Main function to Function1, Now the state of the Main function is stored in Stack, and execution of the Main function is continued when the Function 1 returns. The Fucntion1 Calls Function2 now the State of the Function1 is stored stack and execution of Function 1 will be continued when Function 2 returns.
Consider the below Example of the function call. The Function SumOfSquares function calls the Function Square which returns the square of the number.
Python3
def
Square[X]:
return
[X
*
X]
def
SumofSquares[Array, n]:
Sum
=
0
for
i
in
range
[n]:
SquaredValue
=
Square[Array[i]]
Sum
+
=
SquaredValue
return
Sum
Array
=
[
1
,
2
,
3
,
4
,
5
,
6
,
7
,
8
,
9
,
10
]
n
=
len
[Array]
Total
=
SumofSquares[Array, n]
print
["
Sum
of the Square of
List
of Numbers:", Total]
Output :
Sum of the Square of List of Numbers: 385
Calling Function From another Function within Same class –
In the below example, the class method Function1 calls method Function2 from the class.
Python3
class
Main:
def
__init__[
self
]:
self
.String1
=
"Hello"
self
.String2
=
"World"
def
Function1[
self
]:
self
.Function2[]
print
["Function1 : ",
self
.String2]
return
def
Function2[
self
]:
print
["Function2 : ",
self
.String1]
return
Object
=
Main[]
Object
.Function1[]
Output :
Function2 : Hello Function1 : World
Calling parent class Function from Child class Function –
Consider the below example the child class method invokes the parent class
method. The child class inherits the attributes from the parent class.
Python3
class
Parent:
def
__init__[
self
]:
self
.String1
=
"Hello"
self
.String2
=
"World"
def
Function2[
self
]:
print
["Function2 : ",
self
.String1]
return
class
Child[Parent]:
def
Function1[
self
]:
self
.Function2[]
print
["Function1 : ",
self
.String2]
return
Object1
=
Parent[]
Object2
=
Child[]
Object2.Function1[]
Output :
Function2 : Hello Function1 : World