Variables scope¶
Local variables¶
When a variable is defined inside a function, it isn’t accessible outside this function.
Example :
def foo():
y = "local"
foo()
print(y)
Returns NameError: name 'y' is not defined
Global variables¶
A global variable is created outside the function and declared as global inside the function with the global keyword :
x = "global"
def foo():
# make 'x' inside the function is the same as 'x' outside the function
global x
y = "local"
x = x * 2
print(x)
print(y)
foo()
However a variable initialized outside the funtion is accessible in “read” mode inside the function :
x = "global x"
def foo():
y = x
print(y)
foo()
This works as long as we do not write to x inside the function with x = ..., which would define a new x local variable. To write, inside an function, to a variable defined outside a function, use the global keyword.
Objects scope¶
Inside a function, one can call an object’s method to modify it without declaring this object as global.
Attributes changes can also be made without delaring the object global
def ajouter(liste, valeur_a_ajouter):
liste.append(valeur_a_ajouter)
ma_liste=['a', 'e', 'i']
ajouter(ma_liste, 'o')
print(ma_liste)
# returns : ['a', 'e', 'i', 'o']
References¶
References copy¶
object1 = object2 doesn’t create a copy of object1 to a new object object2 but only copies the reference.
Example :
list1 = [1,2,3]
list2 = list1
list1.append(4)
print(list1)
print(list2)
Returns :
[1, 2, 3, 4]
[1, 2, 3, 4]
Which proves that list1 and list2 point to the same content
Content copy¶
To make list2 a separate copy of list1 :
list1 = [1,2,3]
list2 = list(list1)
list1.append(4)
print(list1)
print(list2)
Returns :
[1, 2, 3, 4]
[1, 2, 3]
list1 and list2 point to a separate content.
Content comparison / Reference comparison¶
ma_liste1 = [1, 2]
ma_liste2 = [1, 2]