Usage of self inside instance methods in Python
I have a class like this
class Test:
def __init__(self, var):
self.var = var
def test(self):
x = self.var + 2
return x
And then I make a class like this
class Test:
def __init__(self, var):
self.var = var
def test(self):
self.x = self.var + 2
return self.x
I understand that I can use self to separate attribute values across various instances of this class. My question is, if I create many utility variables (like x) inside a method, should I always create them using self?
Can anyone explain how the above two classes behave differently (if they do)?
python class oop object
asked Nov 14 '18 at 19:10
BrickomakBrickomak
102
|
show 1 more comment
I have a class like this
class Test:
def __init__(self, var):
self.var = var
def test(self):
x = self.var + 2
return x
And then I make a class like this
class Test:
def __init__(self, var):
self.var = var
def test(self):
self.x = self.var + 2
return self.x
I understand that I can use self to separate attribute values across various instances of this class. My question is, if I create many utility variables (like x) inside a method, should I always create them using self?
Can anyone explain how the above two classes behave differently (if they do)?
python class oop object
asked Nov 14 '18 at 19:10
BrickomakBrickomak
102
Not clear what you are asking.xin the first example is not an attribute; it's just a local variable. Unless you need a value that persists across method calls, prefer the local variable.
– chepner
Nov 14 '18 at 19:13
If you're going to use thexvalue in more than one method, then it should be bound toselfand this initial definition ofself.xshould be done in the__init__method
– JacobIRR
Nov 14 '18 at 19:14
@JacobIRR I'll use it inside just one method.
– Brickomak
Nov 14 '18 at 19:17
1
Usingselfdoes not create a local variable. If you want a local variable, where the value goes away at the end of the method, then use a local variable (noself). If you want an instance attribute, where the value is retained on the instance after the method finishes, then use an instance attribute (withself).
– kindall
Nov 14 '18 at 19:17
in that case, no need to useself.
– JacobIRR
Nov 14 '18 at 19:17
|
show 1 more comment
I have a class like this
class Test:
def __init__(self, var):
self.var = var
def test(self):
x = self.var + 2
return x
And then I make a class like this
class Test:
def __init__(self, var):
self.var = var
def test(self):
self.x = self.var + 2
return self.x
I understand that I can use self to separate attribute values across various instances of this class. My question is, if I create many utility variables (like x) inside a method, should I always create them using self?
Can anyone explain how the above two classes behave differently (if they do)?
python class oop object
asked Nov 14 '18 at 19:10
BrickomakBrickomak
102
I have a class like this
class Test:
def __init__(self, var):
self.var = var
def test(self):
x = self.var + 2
return x
And then I make a class like this
class Test:
def __init__(self, var):
self.var = var
def test(self):
self.x = self.var + 2
return self.x
I understand that I can use self to separate attribute values across various instances of this class. My question is, if I create many utility variables (like x) inside a method, should I always create them using self?
Can anyone explain how the above two classes behave differently (if they do)?
python class oop object
python class oop object
asked Nov 14 '18 at 19:10
BrickomakBrickomak
102
asked Nov 14 '18 at 19:10
BrickomakBrickomak
102
asked Nov 14 '18 at 19:10
BrickomakBrickomak
102
asked Nov 14 '18 at 19:10
BrickomakBrickomak
102
asked Nov 14 '18 at 19:10
BrickomakBrickomak
102
102
Not clear what you are asking.xin the first example is not an attribute; it's just a local variable. Unless you need a value that persists across method calls, prefer the local variable.
– chepner
Nov 14 '18 at 19:13
If you're going to use thexvalue in more than one method, then it should be bound toselfand this initial definition ofself.xshould be done in the__init__method
– JacobIRR
Nov 14 '18 at 19:14
@JacobIRR I'll use it inside just one method.
– Brickomak
Nov 14 '18 at 19:17
1
Usingselfdoes not create a local variable. If you want a local variable, where the value goes away at the end of the method, then use a local variable (noself). If you want an instance attribute, where the value is retained on the instance after the method finishes, then use an instance attribute (withself).
– kindall
Nov 14 '18 at 19:17
in that case, no need to useself.
– JacobIRR
Nov 14 '18 at 19:17
|
show 1 more comment
Not clear what you are asking.xin the first example is not an attribute; it's just a local variable. Unless you need a value that persists across method calls, prefer the local variable.
– chepner
Nov 14 '18 at 19:13
If you're going to use thexvalue in more than one method, then it should be bound toselfand this initial definition ofself.xshould be done in the__init__method
– JacobIRR
Nov 14 '18 at 19:14
@JacobIRR I'll use it inside just one method.
– Brickomak
Nov 14 '18 at 19:17
1
Usingselfdoes not create a local variable. If you want a local variable, where the value goes away at the end of the method, then use a local variable (noself). If you want an instance attribute, where the value is retained on the instance after the method finishes, then use an instance attribute (withself).
– kindall
Nov 14 '18 at 19:17
in that case, no need to useself.
– JacobIRR
Nov 14 '18 at 19:17
Not clear what you are asking.
x in the first example is not an attribute; it's just a local variable. Unless you need a value that persists across method calls, prefer the local variable.– chepner
Nov 14 '18 at 19:13
Not clear what you are asking.
x in the first example is not an attribute; it's just a local variable. Unless you need a value that persists across method calls, prefer the local variable.– chepner
Nov 14 '18 at 19:13
If you're going to use the
x value in more than one method, then it should be bound to self and this initial definition of self.x should be done in the __init__ method– JacobIRR
Nov 14 '18 at 19:14
If you're going to use the
x value in more than one method, then it should be bound to self and this initial definition of self.x should be done in the __init__ method– JacobIRR
Nov 14 '18 at 19:14
@JacobIRR I'll use it inside just one method.
– Brickomak
Nov 14 '18 at 19:17
@JacobIRR I'll use it inside just one method.
– Brickomak
Nov 14 '18 at 19:17
1
1
Using
self does not create a local variable. If you want a local variable, where the value goes away at the end of the method, then use a local variable (no self). If you want an instance attribute, where the value is retained on the instance after the method finishes, then use an instance attribute (with self).– kindall
Nov 14 '18 at 19:17
Using
self does not create a local variable. If you want a local variable, where the value goes away at the end of the method, then use a local variable (no self). If you want an instance attribute, where the value is retained on the instance after the method finishes, then use an instance attribute (with self).– kindall
Nov 14 '18 at 19:17
in that case, no need to use
self.– JacobIRR
Nov 14 '18 at 19:17
in that case, no need to use
self.– JacobIRR
Nov 14 '18 at 19:17
|
show 1 more comment
1 Answer
1
active
oldest
votes
Let's see the difference between the two classes :
class Test:
def __init__(self, var):
self.var = var
def test(self):
x = self.var + 2
return x
Let's create a Test object:
t = Test(1)
And see what we can do
t.var # 1
t.x # Raises AttributeError : no such attribute in the class
t.test() #3
t.x # Still erroring
And with your second class
class Test:
def __init__(self, var):
self.var = var
def test(self):
self.x = self.var + 2
return self.x
Let's create a Test object:
t = Test(1)
And see what we can do
t.var # 1
t.x # Raises AttributeError : no such attribute in the class
t.test() #3
t.x # 3
So what ? Well we can see that any variables defined with self.VARNAME persist in the instance, while simple local variables, without self., dosen't.
However, if x needs to be accessible with t.x, i'd probably go for a property, like so
class Test:
def __init__(self, var):
self.var = var
@property
def x(self):
x = self.var + 2
return x
t = Test()
t.x # 3
answered Nov 14 '18 at 19:17
WayToDoorWayToDoor
536317
add a comment |
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1 Answer
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active
oldest
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oldest
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active
oldest
votes
Let's see the difference between the two classes :
class Test:
def __init__(self, var):
self.var = var
def test(self):
x = self.var + 2
return x
Let's create a Test object:
t = Test(1)
And see what we can do
t.var # 1
t.x # Raises AttributeError : no such attribute in the class
t.test() #3
t.x # Still erroring
And with your second class
class Test:
def __init__(self, var):
self.var = var
def test(self):
self.x = self.var + 2
return self.x
Let's create a Test object:
t = Test(1)
And see what we can do
t.var # 1
t.x # Raises AttributeError : no such attribute in the class
t.test() #3
t.x # 3
So what ? Well we can see that any variables defined with self.VARNAME persist in the instance, while simple local variables, without self., dosen't.
However, if x needs to be accessible with t.x, i'd probably go for a property, like so
class Test:
def __init__(self, var):
self.var = var
@property
def x(self):
x = self.var + 2
return x
t = Test()
t.x # 3
answered Nov 14 '18 at 19:17
WayToDoorWayToDoor
536317
add a comment |
Let's see the difference between the two classes :
class Test:
def __init__(self, var):
self.var = var
def test(self):
x = self.var + 2
return x
Let's create a Test object:
t = Test(1)
And see what we can do
t.var # 1
t.x # Raises AttributeError : no such attribute in the class
t.test() #3
t.x # Still erroring
And with your second class
class Test:
def __init__(self, var):
self.var = var
def test(self):
self.x = self.var + 2
return self.x
Let's create a Test object:
t = Test(1)
And see what we can do
t.var # 1
t.x # Raises AttributeError : no such attribute in the class
t.test() #3
t.x # 3
So what ? Well we can see that any variables defined with self.VARNAME persist in the instance, while simple local variables, without self., dosen't.
However, if x needs to be accessible with t.x, i'd probably go for a property, like so
class Test:
def __init__(self, var):
self.var = var
@property
def x(self):
x = self.var + 2
return x
t = Test()
t.x # 3
answered Nov 14 '18 at 19:17
WayToDoorWayToDoor
536317
add a comment |
Let's see the difference between the two classes :
class Test:
def __init__(self, var):
self.var = var
def test(self):
x = self.var + 2
return x
Let's create a Test object:
t = Test(1)
And see what we can do
t.var # 1
t.x # Raises AttributeError : no such attribute in the class
t.test() #3
t.x # Still erroring
And with your second class
class Test:
def __init__(self, var):
self.var = var
def test(self):
self.x = self.var + 2
return self.x
Let's create a Test object:
t = Test(1)
And see what we can do
t.var # 1
t.x # Raises AttributeError : no such attribute in the class
t.test() #3
t.x # 3
So what ? Well we can see that any variables defined with self.VARNAME persist in the instance, while simple local variables, without self., dosen't.
However, if x needs to be accessible with t.x, i'd probably go for a property, like so
class Test:
def __init__(self, var):
self.var = var
@property
def x(self):
x = self.var + 2
return x
t = Test()
t.x # 3
answered Nov 14 '18 at 19:17
WayToDoorWayToDoor
536317
Let's see the difference between the two classes :
class Test:
def __init__(self, var):
self.var = var
def test(self):
x = self.var + 2
return x
Let's create a Test object:
t = Test(1)
And see what we can do
t.var # 1
t.x # Raises AttributeError : no such attribute in the class
t.test() #3
t.x # Still erroring
And with your second class
class Test:
def __init__(self, var):
self.var = var
def test(self):
self.x = self.var + 2
return self.x
Let's create a Test object:
t = Test(1)
And see what we can do
t.var # 1
t.x # Raises AttributeError : no such attribute in the class
t.test() #3
t.x # 3
So what ? Well we can see that any variables defined with self.VARNAME persist in the instance, while simple local variables, without self., dosen't.
However, if x needs to be accessible with t.x, i'd probably go for a property, like so
class Test:
def __init__(self, var):
self.var = var
@property
def x(self):
x = self.var + 2
return x
t = Test()
t.x # 3
answered Nov 14 '18 at 19:17
WayToDoorWayToDoor
536317
answered Nov 14 '18 at 19:17
WayToDoorWayToDoor
536317
answered Nov 14 '18 at 19:17
WayToDoorWayToDoor
536317
answered Nov 14 '18 at 19:17
WayToDoorWayToDoor
536317
536317
add a comment |
add a comment |
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Not clear what you are asking.
xin the first example is not an attribute; it's just a local variable. Unless you need a value that persists across method calls, prefer the local variable.– chepner
Nov 14 '18 at 19:13
If you're going to use the
xvalue in more than one method, then it should be bound toselfand this initial definition ofself.xshould be done in the__init__method– JacobIRR
Nov 14 '18 at 19:14
@JacobIRR I'll use it inside just one method.
– Brickomak
Nov 14 '18 at 19:17
1
Using
selfdoes not create a local variable. If you want a local variable, where the value goes away at the end of the method, then use a local variable (noself). If you want an instance attribute, where the value is retained on the instance after the method finishes, then use an instance attribute (withself).– kindall
Nov 14 '18 at 19:17
in that case, no need to use
self.– JacobIRR
Nov 14 '18 at 19:17