Assigning a function to a variable
Question:
Let’s say I have a function
def x():
print(20)
Now I want to assign the function to a variable called y
, so that if I use the y
it calls the function x
again. if i simply do the assignment y = x()
, it returns None
.
Answers:
You simply don’t call the function.
>>> def x():
>>> print(20)
>>> y = x
>>> y()
20
The brackets tell Python that you are calling the function, so when you put them there, it calls the function and assigns y
the value returned by x
(which in this case is None
).
When you assign a function to a variable you don’t use the () but simply the name of the function.
In your case given def x(): ...
, and variable silly_var
you would do something like this:
silly_var = x
and then you can call the function either with
x()
or
silly_var()
when you perform y=x()
you are actually assigning y to the result of calling the function object x
and the function has a return value of None
. Function calls in python are performed using ()
. To assign x to y
so you can call y
just like you would x
you assign the function object x to y like y=x
and call the function using y()
lambda should be useful for this case.
For example,
-
create function y=x+1
y=lambda x:x+1
-
call the function
y(1)
then return 2
.
The syntax
def x():
print(20)
is basically the same as x = lambda: print(20)
(there are some differences under the hood, but for most pratical purposes, the results the same).
The syntax
def y(t):
return t**2
is basically the same as y= lambda t: t**2
. When you define a function, you’re creating a variable that has the function as its value. In the first example, you’re setting x
to be the function lambda: print(20)
. So x
now refers to that function. x()
is not the function, it’s the call of the function. In python, functions are simply a type of variable, and can generally be used like any other variable. For example:
def power_function(power):
return lambda x : x**power
power_function(3)(2)
This returns 8. power_function
is a function that returns a function as output. When it’s called on 3
, it returns a function that cubes the input, so when that function is called on the input 2
, it returns 8. You could do cube = power_function(3)
, and now cube(2)
would return 8.
I don’t know what is the value/usefulness of renaming a function and call it with the new name. But using a string as function name, e.g. obtained from the command line, has some value/usefulness:
import sys
fun = eval(sys.argv[1])
fun()
In the present case, fun = x.
def x():
print(20)
return 10
y = x
y()
print(y)
gives the output
20
<function x at 0x7fc548cd3040>
so it does not actually assign the value returned by x() to the variable y.
Let’s say I have a function
def x():
print(20)
Now I want to assign the function to a variable called y
, so that if I use the y
it calls the function x
again. if i simply do the assignment y = x()
, it returns None
.
You simply don’t call the function.
>>> def x():
>>> print(20)
>>> y = x
>>> y()
20
The brackets tell Python that you are calling the function, so when you put them there, it calls the function and assigns y
the value returned by x
(which in this case is None
).
When you assign a function to a variable you don’t use the () but simply the name of the function.
In your case given def x(): ...
, and variable silly_var
you would do something like this:
silly_var = x
and then you can call the function either with
x()
or
silly_var()
when you perform y=x()
you are actually assigning y to the result of calling the function object x
and the function has a return value of None
. Function calls in python are performed using ()
. To assign x to y
so you can call y
just like you would x
you assign the function object x to y like y=x
and call the function using y()
lambda should be useful for this case.
For example,
-
create function y=x+1
y=lambda x:x+1
-
call the function
y(1)
then return2
.
The syntax
def x():
print(20)
is basically the same as x = lambda: print(20)
(there are some differences under the hood, but for most pratical purposes, the results the same).
The syntax
def y(t):
return t**2
is basically the same as y= lambda t: t**2
. When you define a function, you’re creating a variable that has the function as its value. In the first example, you’re setting x
to be the function lambda: print(20)
. So x
now refers to that function. x()
is not the function, it’s the call of the function. In python, functions are simply a type of variable, and can generally be used like any other variable. For example:
def power_function(power):
return lambda x : x**power
power_function(3)(2)
This returns 8. power_function
is a function that returns a function as output. When it’s called on 3
, it returns a function that cubes the input, so when that function is called on the input 2
, it returns 8. You could do cube = power_function(3)
, and now cube(2)
would return 8.
I don’t know what is the value/usefulness of renaming a function and call it with the new name. But using a string as function name, e.g. obtained from the command line, has some value/usefulness:
import sys
fun = eval(sys.argv[1])
fun()
In the present case, fun = x.
def x():
print(20)
return 10
y = x
y()
print(y)
gives the output
20
<function x at 0x7fc548cd3040>
so it does not actually assign the value returned by x() to the variable y.