Why is it string.join(list) instead of list.join(string)?

Question

This actually confused me a lot. The below code is better:

my_list = ["Hello", "world"]

print(my_list.join("-"))

# Produce: "Hello-world"

than:

my_list = ["Hello", "world"]

print("-".join(my_list))

# Produce: "Hello-world"

I just want to know, whether is there any reason for being like this?

Answer 1

This is because that any iterable can be combined (e.g, list, tuple, dict, set), however, its substance and the "joiner" should be strings

Example:

'_'.join(['welcome', 'to', 'stack', 'overflow'])

'_'.join(('welcome', 'to', 'stack', 'overflow'))

'welcome_to_stack_overflow'

When you try to use other than string, it will raise the accompanying error:

TypeError: sequence item 0: expected str instance, int found

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