Is not empty in python?
Short Answer:Place the list in a boolean context (for example, with an
PEP 8PEP 8, the official Python style guide for Python code in Python's standard library, asserts:
We should expect that standard library code should be as performant and correct as possible. But why is that the case, and why do we need this guidance? ExplanationI frequently see code like this from experienced programmers new to Python:
And users of lazy languages may be tempted to do this:
These are correct in their respective other languages. And this is even semantically correct in Python. But we consider it un-Pythonic because Python supports these semantics directly in the list object's interface via boolean coercion. From the docs (and note specifically the inclusion of the
empty list,
And the datamodel documentation:
and
So instead of this:
or this:
Do this:
Doing what's Pythonic usually pays off in performance:Does it pay off? (Note that less time to perform an equivalent operation is better:)
For scale, here's the cost of calling the function and constructing and returning an empty list, which you might subtract from the costs of the emptiness checks used above:
We see that either checking for length
with the builtin function Why? For the First Python has to check the globals to see if Then it must call the function, load
And for the
The "Pythonic" way is a much simpler and faster check since the length of the list is cached in the object instance header:
Evidence from the C source and documentation
From the c source in Include/listobject.h:
Response to comments:
IPython magic,
We can see there's a bit of linear cost for each additional
Now let's look at the case for an unempty list:
What we can see here is that it makes little difference whether you pass in an actual Python is written in C; it uses its logic at the C level. Anything you write in Python will be slower. And it will likely be orders of magnitude slower unless you're using the mechanisms built into Python directly. How do you check if a field is empty in Python?Use an if statement to check if a user input is empty, e.g. if country == '': . The input() function is guaranteed to return a string, so if it returns an empty string, the user didn't enter a value.
Is empty string none in Python?The None value is not an empty string in Python, and neither is (spaces).
What is a non empty list in Python?In Python, empty lists evaluate False , and non-empty lists evaluate True in boolean contexts. Therefore, you can simply treat the list as a predicate returning a Boolean value. This solution is highly Pythonic and recommended by the PEP8 style guide.
How check string is null or not in Python?Use len to Check if a String in Empty in Python
Let's see how we can use this function to check if a string is empty or not: # Using len() To Check if a String is Empty string = '' if len(string) == 0: print("Empty string!") else: print("Not empty string!") # Returns # Empty string!
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