Overview:
- del statement removes a name from a scope.
- After del statement is applied on a name, identity is lost for that name. Any reference to it afterwards will raise an exception of type NameError.
- del statement can be applied in several contexts:
Example - Removing a name from local and global scopes:
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# Python example program to remove names from global and local # scopes using the Python keyword del today = "Sunday";
def oddSequence(): sum = 0; for i in range(1, 10, 2): print(i); sum = sum + i;
# Prints the last value again print(i);
# Print sum print("Sum %d"%sum);
# Remove sum from local scope try: del sum; print(sum); except Exception as Ex: print(Ex);
# Remove today from global scope global today; del today;
# Remove i from local scope del i;
# Already i has been unbound try: print(i); except Exception as Ex: print(Ex);
oddSequence();
# Today no longer available at global scope print(today); |
Output:
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1 3 5 7 9 9 Sum 25 local variable 'sum' referenced before assignment local variable 'i' referenced before assignment Traceback (most recent call last): File "del0.py", line 40, in <module> print(today); NameError: name 'today' is not defined |
Example - Removing a reference to a class instance from global scope:
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# Example program that removes an object from # the global scope class X: def __init__(self, val): self.val = val
class Y: def __init__(self, val): self.val = val
class A: def __init__(self, x, y): self.x = x self.y = y
# Create instances of X and Y x = X("one"); y = Y("two");
# Create instances of A. # Instances of A have references to x and y instances. a1 = A(x,y); a2 = A(x,y);
# Removes a1 recursively. It will not remove object x from the scope. del a1; print(a2.x.val); # Raises NameError print(a1); |
Overview:
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one Traceback (most recent call last): File "del1.py", line 29, in <module> print(a1); NameError: name 'a1' is not defined |
Example - Removing a class attribute:
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class Robot: def __init__(self, id): self.id = id;
def greet(self): print("Hello");
r1 = Robot("R1"); r1.greet();
# Delete the id attribute...possible del r1.id; try: print(r1.id); # Now id is no longer part of r1 instance except Exception as Ex: print(Ex)
print("hi"); # Delete the function object - greet(), not possible del r1.greet; |
Output:
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Hello 'Robot' object has no attribute 'id' hi Traceback (most recent call last): File "del2.py", line 20, in <module> del r1.greet; AttributeError: greet |
Example - Removing elements from Python iterables - list, dictionary using del:
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# Python example program to delete elements from iterables listObject = [5, 10, 15, 20, 25]; tupleObject = (2, 4, 6, 8, 10); mapObject = {1:"One", 2:"Two", 3:"Three", 4:"Four", 5:"Five", 6:"Six"};
# Remove an element from a Python list print("Length of the list before removal of an element:%d"%len(listObject)); del listObject[0]; print("Length of the list after removal of an element:%d"%len(listObject));
# Remove a key and the corresponding value from a Python dictionary print("Length of the dictionary before removal of an element:%d"%len(mapObject)); del mapObject[2]; print("Length of the dictionary after removal of an element:%d"%len(mapObject));
# Removal of an element from an immutable sequence is not possible del tupleObject[1]; |
Output:
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Length of the list before removal of an element:5 Length of the list after removal of an element:4 Length of the dictionary before removal of an element:6 Length of the dictionary after removal of an element:5 Traceback (most recent call last): File "del_elem.py", line 17, in <module> del tupleObject[1]; TypeError: 'tuple' object doesn't support item deletion |