You cannot assign to a list like xs[i] = value, unless the list already is initialized with at least i+1 elements (because the first index is 0). Instead, use xs.append(value) to add elements to the end of the list. (Though you could use the assignment notation if you were using a dictionary instead of a list.)
Creating an empty list:
>>> xs = [None] * 10
>>> xs
[None, None, None, None, None, None, None, None, None, None]
Assigning a value to an existing element of the above list:
>>> xs[1] = 5
>>> xs
[None, 5, None, None, None, None, None, None, None, None]
Keep in mind that something like xs[15] = 5 would still fail, as our list has only 10 elements.
range(x) creates a list from [0, 1, 2, ... x-1]
# 2.X only. Use list(range(10)) in 3.X.
>>> xs = range(10)
>>> xs
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
Using a function to create a list:
>>> def display():
... xs = []
... for i in range(9): # This is just to tell you how to create a list.
... xs.append(i)
... return xs
...
>>> print display()
[0, 1, 2, 3, 4, 5, 6, 7, 8]
List comprehension (Using the squares because for range you don't need to do all this, you can just return range(0,9) ):
>>> def display():
... return [x**2 for x in range(9)]
...
>>> print display()
[0, 1, 4, 9, 16, 25, 36, 49, 64]
You cannot assign to a list like xs[i] = value, unless the list already is initialized with at least i+1 elements (because the first index is 0). Instead, use xs.append(value) to add elements to the end of the list. (Though you could use the assignment notation if you were using a dictionary instead of a list.)
Creating an empty list:
>>> xs = [None] * 10
>>> xs
[None, None, None, None, None, None, None, None, None, None]
Assigning a value to an existing element of the above list:
>>> xs[1] = 5
>>> xs
[None, 5, None, None, None, None, None, None, None, None]
Keep in mind that something like xs[15] = 5 would still fail, as our list has only 10 elements.
range(x) creates a list from [0, 1, 2, ... x-1]
# 2.X only. Use list(range(10)) in 3.X.
>>> xs = range(10)
>>> xs
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
Using a function to create a list:
>>> def display():
... xs = []
... for i in range(9): # This is just to tell you how to create a list.
... xs.append(i)
... return xs
...
>>> print display()
[0, 1, 2, 3, 4, 5, 6, 7, 8]
List comprehension (Using the squares because for range you don't need to do all this, you can just return range(0,9) ):
>>> def display():
... return [x**2 for x in range(9)]
...
>>> print display()
[0, 1, 4, 9, 16, 25, 36, 49, 64]
Try this instead:
lst = [None] * 10
The above will create a list of size 10, where each position is initialized to None. After that, you can add elements to it:
lst = [None] * 10
for i in range(10):
lst[i] = i
Admittedly, that's not the Pythonic way to do things. Better do this:
lst = []
for i in range(10):
lst.append(i)
Or even simpler, in Python 2.x you can do this to initialize a list with values from 0 to 9:
lst = range(10)
And in Python 3.x:
lst = list(range(10))
python - How do I check if a list is empty? - Stack Overflow
How can I make an empty list of size 4 in python? - Stack Overflow
[deleted by user]
python - Does empty list have a length? - Stack Overflow
if not a:
print("List is empty")
Using the implicit booleanness of the empty list is quite Pythonic.
The Pythonic way to do it is from the PEP 8 style guide.
For sequences, (strings, lists, tuples), use the fact that empty sequences are false:
# Correct: if not seq: if seq: # Wrong: if len(seq): if not len(seq):
The List in Python is not an Array of fixed-size upon declaration, so it is by design variable in size. Meaning you can just append members into it. Much like ArrayLists in Java!
So if the context of your question(I am just guessing here) is to find ways to limit the size of a particular List in Python, you would have to do it elsewhere, not during declaration.
Useful reference for this topic: https://www.delftstack.com/howto/python/python-initialize-empty-list/
How can I make an empty list of size 4 in python?
You must not, as these are mutually exclusive requirements: to have list which is empty (i.e. has size 0) and has size 4