I have a list:
roll = [1, 2, 3]
For converting each of the element into a string, can we directly do roll = str(roll) rather that iterating over it and calling str() on each element? Is this a correct way?
I am new to Python, any hint in the right direction will do!
That wouldn't work, since that would convert the entire list into one string:
roll = [1, 2, 3]
roll = str(roll)
print(roll)
# Prints [1, 2, 3]
print(type(roll))
# Prints <class 'str'>
You can instead use a list comprehension, to convert each item in the list one by one:
roll = [1, 2, 3]
roll = [str(r) for r in roll]
print(roll)
# Prints ['1', '2', '3']
print(type(roll))
# Prints <class 'list'>
Thinking in terms of types, the original variable you have is of type List[int] ([1, 2, 3]).
When using the str function, the result is an element of type str (aka '[1, 2, 3]'), but that's not the result that you want since you want to convert each individual element in the list to str, which makes the desired type to be List[str] (['1', '2', '3']).
In python, there are several canonical ways to apply a function to each individual element:
new_roll = [str(x) for x in roll] # ['1', '2', '3']
This method is the simplest. It is basically a one-liner that does the followings:
new_roll = []
for x in roll:
new_roll.append(str(x))
Notice that the original variable roll won't be mutated since it is creating a new list.
Another way to do the same thing is by using the map function in python. However for efficiency reason, the type of the output is of type Map[str] instead of type List[str].
roll_map = map(str, roll)
for x in roll_map:
print(x)
It is basically doing the followings:
roll = [1, 2, 3]
for x in roll:
str_x = str(x)
print(str_x)
Notice that no new list has been created in order to save memory. This method is generally applicable when you need the result of a function applied to a list (or an iterator in general) but you do not want to store the results of the function application (to save memory).
A common hack to obtain a list via the map function is by list(map(str, roll)).
Yes, this can be done without iterating over it using loop in following way:
roll = list(map(str, roll))
roll_str = [str(n) for n in roll]