Python join: why is it string.join(list) instead of list.join(string)?

Question

This has always confused me. It seems like this would be nicer: my_list = ["Hello", "world"] print my_list.join("-") # Produce: "Hello-world"Than this: my_list = ["Hello", "world"] print "-".join(my_list) # Produce: "Hello-world"Is there a specific reason it is like this?

Answer 1

Well, keep in mind that the join() and split() methods complement each other on the str class ... split() generates a list of "fields" (substrings) based on a token, and join() merges a list of strings in an iterable around a given token or field delimiter ...

It makes more sense in that context: 2 complimentary services offered by str: one returns a list while the other accepts a list.

fields = ['I', 'like', 'Python']

record = '-'.join(fields )

fields=record.split(sep='-')

Also keep in mind that the iterable passed to join() should be limited to str elements ...

Something like this will cause you problems:

nums=[1,2,3]

'-'.join(nums)

Traceback (most recent call last):

File "<pyshell#3>", line 1, in <module>

'-'.join(nums)

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