Access a Python variable which is inside a function, in another function

Question

Let's say I have a function:

func1():
    do something
    a,b = somevalues,somevalues

Now let's say I have another function:

func2():
    do something

I would now like to now use a,b in func2() which were calculated inside func1() .

I tried using

func1():
    do something
    a,b = somevalues, somevalues
    func1.a = somevalues
    func1.b = somevalues

func1()
func1.a

But using this, I have to each time run func1() before using a,b.

func1() also creates some plots along with calculating a,b.

So is it possible to utilise a,b in func2() without calling func1() ?

Can you return a,b from func1() and then pass them as arguments to func2()? — robert
– robert, Commented Sep 21, 2015 at 12:33
You need to rethink your code structure. If you need a and b independently of func1() then they should not be declared within it. — michaelrccurtis
– michaelrccurtis, Commented Sep 21, 2015 at 12:34
@michaelrccurtis: But I calculate them inside the func1() as I needed them for several plots inside func1(). So you are suggesting me to calculate them outside the function? — Srivatsan
– Srivatsan, Commented Sep 21, 2015 at 12:35
@ThePredator Yes, exactly. You could store them as member variables of a class, for example, if that makes sense given their meaning. — michaelrccurtis
– michaelrccurtis, Commented Sep 21, 2015 at 12:36

robert · Accepted Answer · 2015-09-21 12:35:38Z

5

This may be what you want. Also, I suggest you work through an introductory Python tutorial.

func1():
    #do something
    a,b = somevalues, somevalues
    return a, b

func2(a, b):
    #do something on a and b

a, b = func1()
func2(a, b)

answered Sep 21, 2015 at 12:35

robert

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1 Comment

Srivatsan Over a year ago

I accept this as an answer for now! But as pointed out by @michaelrccurtis, I shall try to restructure my code!

Community · Accepted Answer · 2017-05-23 11:58:08Z

2

The answer by robert is probably the easiest way to do what your want. Here is another:

class class1():
    a,b = somevalues, somevalues
    @staticmethod
    def func1():
        do something

func2(class1.a, class1.b)
class1.func1()

The reason this works and your way doesn't work has to do with the way Python treats functions and classes.

The body of a function is not executed until it is called the first time. So when you have:

def func1():
    func1.a = somevalue

...you cannot access func1.a until func1 has been called at least once, as you have already discovered.

However, for classes, the body of the class runs when the code is compiled. So that when you do:

class example:
    a = somevalue

...you are able to access example.a immediately.

EDIT:

Answering the question in the comments: access func1, a, or b as shown above using the class itself (in Python, classes ARE objects, just like any other object):

class1.a
class1.func1()

You could also make a shortcut for yourself:

func1 = class1.func1
func1()

Another way to do things- so that you could have different versions of a and b- be to make a and b instance attributes instead of class attributes.

class class1:
    def __init__(self, a, b):
        self.a, self.b = a, b
    @staticmethod
    def func1():
        dosomething

obj1 = class1(somevalue1A, somevalue1B)
obj2 = class1(somevalue2A, somevalue2B)
func2(obj1.a, obj1.b)
func2(obj2.a, obj2.b)
obj1.func1()
obj2.func1()
class1.func1()

The last three lines all call the same function, because obj1.func1, obj2.func1, and class1.func1 all point to the same method of class1. Note that the reason you can call func1 from both the class (class1) and the instances (obj1, obj2) of the class is that func1 is a static method.

edited May 23, 2017 at 11:58

CommunityBot

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answered Sep 21, 2015 at 12:50

Rick

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4 Comments

Srivatsan Over a year ago

I understand now! But in this case, how do I call func1() ? Do I need to use the class and call it or can I call it directly like func1() ?

Rick Over a year ago

You can use the class to call it since it is a static method of the class, or you can make an instance of the class. I'll add some more explanation.

Rick Over a year ago

@ThePredator I have answered your question in the answer.

Srivatsan Over a year ago

Thank you for your detailed explanation! I shall try to understand it slowly

Psytho · Accepted Answer · 2015-09-21 12:36:15Z

0

func1():
    do something
    a,b = somevalues,somevalues
    return a, b

x, y = func1()

Now you can use x and y everywhere without callin func1() every time. For example in func2() this way:

def func2(a, b):
    do something

Then you call func2() with x and y respectivly:

func2(x, y)

answered Sep 21, 2015 at 12:36

Psytho

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2 Comments

Srivatsan Over a year ago

but since func1() create many plots, I don't want to call func1() to access the variables as I need to then close all the plots!

Psytho Over a year ago

Then why do you assign values to a and b in a function that draws a plot?

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