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/
Answer from xhbear on Stack OverflowThe 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
performance - Creating an empty list in Python - Stack Overflow
How do I check if this list is "empty"?
What are empty lists and what are they used for
Allow None in list initializer to return an empty list: list(None) -> [] - Ideas - Discussions on Python.org
Videos
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):
Here is how you can test which piece of code is faster:
% python -mtimeit "l=[]"
10000000 loops, best of 3: 0.0711 usec per loop
% python -mtimeit "l=list()"
1000000 loops, best of 3: 0.297 usec per loop
However, in practice, this initialization is most likely an extremely small part of your program, so worrying about this is probably wrong-headed.
Readability is very subjective. I prefer [], but some very knowledgable people, like Alex Martelli, prefer list() because it is pronounceable.
list() is inherently slower than [], because
there is symbol lookup (no way for python to know in advance if you did not just redefine list to be something else!),
there is function invocation,
then it has to check if there was iterable argument passed (so it can create list with elements from it) ps. none in our case but there is "if" check
In most cases the speed difference won't make any practical difference though.
I'm completely stumped on a computer science assignment because our lecturer has given us zero information. We're supposed to have the user input a list and check if the list is in decreasing order and print a suitable message if it is. That part works fine. However, if the list is "empty" (I'll explain the quotations in a second) then it should print the list is empty.
The problem is that, according to our brief we're supposed to use .split(",") in order to allow the user to separate their numbers with commas. The problem lies in the fact that even if a user hits enter without inputting anything, the list is still '1' long with just an empty string. I've been scouring the web to find out how to check if a list is empty. But all the tutorials have so far just been in relation to actually empty lists (as in, list = []). One did use the all() function to check that all items in the list were strings, which did work and let me print that the list is empty, but broke the original function. Could someone please help me I'm tearing my hair out with this.
--
def checkOrder():
# checks, etc.
integer_list = []
listLength = len(integer_list)
increasing = 0
decreasing = 0
singleValue = 0
# Converting inputted numbers into a split list
userInput = input("Please enter your numbers seperated by a comma (,):")
inputtedStrings = userInput.split(",")
for number in inputtedStrings:
inputtedIntegers = int(number)
integer_list.append(inputtedIntegers)
# Enumerating list
for i, val in enumerate(integer_list[:-1]):
if val <= integer_list[i+1]:
increasing = 1
elif val >= integer_list[i+1]:
decreasing = 1
# Check for a single value
if len(integer_list) == 1:
singleValue = 1
if len(integer_list) == 1 and
print("The list is empty.")
if increasing == 1:
print("The numbers are in increasing order.")
elif decreasing == 1 or singleValue == 1:
print("The numbers are in decreasing order.")
checkOrder()
--
I just started to learn python a couple of weeks ago, I got introduced to this concept of empty lists, I just can't wrap my head around it. Whenever I check on a problem's solution where they use empty lists, I kinda understand why they use it, but whenever I do a problem where empty lists are the solution I can't seem to even think about using an empty list.
Basically I just don't get how empty lists work.