if not a:
print("List is empty")
Using the implicit booleanness of the empty list is quite Pythonic.
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):
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()
--
In shell languages of the Bourne family, the : command, which does nothing at all, is typically used in two situations:
Placeholder for when something expects a mandatory command, e.g.
while some_condtion do : donesince
dorequires at least one command.Discarding the arguments, but performing side effects inside the argument list, e.g.
: ${myvar=foo}
I'm sure there are probably other applications that shell experts would know :)
In Python (and other languages) it's used less frequently. It can act as an argument to a higher-order function when you don't actually want to do anything. For example, say you have a function that submits a form and allows an function to be called asynchronously after submission is complete:
def submit(callback=empty_func):
...
This way, if the callback is not provided, the submission will still go through but no further actions will be performed. If you had used None as the default value, you'd have to explicitly check whether the callback was None, adding clutter to the code.
Rufflewind did a good job covering when you might use an empty function in a completed program. In my experience, it tends to be used more often in unfinished programs, so you can plan out what you're going to write and have it still compile until you get around to actually implementing it. In other words, it's usually just a placeholder.
It's necessary in python's case because it uses indentation to mark blocks, unlike C-like languages who use braces {}. This means if you didn't have pass, the parser couldn't tell if you meant to leave it empty or if you forgot. Including pass makes the parser much simpler, and gives you a convenient word to search for when you're looking for unimplemented blocks.