In this tutorial, we will look at how to check if a list contains only numbers in Python with the help of some examples.
How to check if all list elements are numbers?
You can use a combination of the Python built-in isinstance[] and all[] function to check if a list contains only numbers. For instance, you can use the following steps to check if all elements in a list are integers in Python –
- In a list comprehension, for each element in the list, check if it’s an integer
using the
isinstance[]function. - Apply the Python built-in
all[]function to returnTrueonly if all the items in the above list comprehension correspond toTrue.
The following is the code to check if all elements in a list are integers or not.
# check if all elements in ls are integers all[[isinstance[item, int] for item in ls]]
Let’s take a look at an example.
# list of numbers ls = [1, 2, 3, 4] # check if list contains only numbers print[all[[isinstance[item, int] for item in ls]]]
Output:
True
We get True as the output as all elements in the list ls are integers.
Let’s take a look at another example.
# list of numbers and a string ls = [1, 2, 3, 4, 'cat'] # check if list contains only numbers print[all[[isinstance[item, int] for item in ls]]]
Output:
False
Here we get False as the output because not all elements in the list ls are integers. One element, “cat” in the list is a string.
Check if all items in a list of strings are numeric
If you, however, have a list of strings and want to check whether all the elements in the list are digits or not, you can use the following code.
# list of numeric strings ls = ["1", "2", "3", "4"] # check if list of string contains only numberic elements print[all[[item.isdigit[] for item in ls]]]
Output:
True
Here we check whether each element in the list of
strings, ls is a numerical value or not using the string isdigit[] function. We get True as the output as all the strings in the list ls are numeric characters.
You might also be interested in –
- Python – Check if String Contains Only Numbers
- Python – Check List Contains All Elements Of Another List
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Piyush is a data scientist passionate about using data to understand things better and make informed decisions. In the past, he's worked as a Data Scientist for ZS and holds an engineering degree from IIT Roorkee. His hobbies include watching cricket, reading, and working on side projects.
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The usual way to check whether something can be converted to an int is to try it and see, following the EAFP principle:
try:
int_value = int[string_value]
except ValueError:
# it wasn't an int, do something appropriate
else:
# it was an int, do something appropriate
So, in your case:
for item in mylist:
try:
int_value = int[item]
except ValueError:
pass
else:
mynewlist.append[item] # or append[int_value] if you want numbers
In most cases, a loop around some trivial code that ends with mynewlist.append[item] can be turned into a list comprehension, generator expression, or call to map or filter. But here, you can't, because
there's no way to put a try/except into an expression.
But if you wrap it up in a function, you can:
def raises[func, *args, **kw]:
try:
func[*args, **kw]
except:
return True
else:
return False
mynewlist = [item for item in mylist if not raises[int, item]]
… or, if you prefer:
mynewlist = filter[partial[raises, int], item]
It's cleaner to use it this way:
def raises[exception_types, func, *args, **kw]:
try:
func[*args, **kw]
except exception_types:
return True
else:
return False
This way, you can pass it the exception [or tuple of exceptions] you're expecting, and those will return True, but if any unexpected exceptions are raised, they'll propagate out. So:
mynewlist = [item for item in mylist if not raises[ValueError, int, item]]
… will do what you want, but:
mynewlist = [item for item in mylist if not raises[ValueError, item, int]]
… will raise a TypeError, as it
should.