I would like some further insight in how the function join() works differently when using format(), and a list. As you can tell in the bottom, output is very different.

ina = "{a}{aa}{aaa}{aaaa}".format(a = "This ", aa = "is ", aaa = " my", aaaa = " house.")
print("=".join(ina))

list = "_".join(["Mayor in", "is the", "one to, done"])
print(list)

OUTPUT:

T=h=i=s= =i=s= = =m=y= =h=o=u=s=e=.
Mayor in_is the_one to, done

CodePudding user response：

ina = "{a}{aa}{aaa}{aaaa}".format(a = "This ", aa = "is ", aaa = " my", aaaa = " house.")

ina is now a string: "This is my house".

"=".join(ina)

takes every element of the iterable ina, which is a character, and joins it using =.

["Mayor in", "is the", "one to, done"]

is a list.

"_".join(["Mayor in", "is the", "one to, done"])

takes every element of the iterable ["Mayor in", "is the", "one to, done"], which is a string, and joins it using _.

Joining a string (with character as elements) and joining a list (with strings as elements) will typically give different results, unless your list happens to have single characters in it.

As an aside, using list as a variable name in Python is a bad practice: list already has a value. Should some other place in code use list intending to access the list type, the code would fail.

CodePudding user response：

This is because strings are stored as lists of characters. In the first example, ina = "This is my house." which behind the scenes is stored as ['T', 'h', 'i', 's', ' ', 'm', 'y', ' ', 'h', etc.], so join inserts the '=' between each element of the array giving the output you saw.

The second example where you have a list of strings (aka a list of lists of characters) is stored as [['M', 'a', 'y', 'o', 'r', ' ', 'i', 'n'], ['i', 's', ' ', t', 'h', 'e'], ['o', ...]]. join() only operates on the outermost list, so it will only insert '_' in 2 places.

One way you can see this is by using the len() function.

len(ina) would be 18, but len(["Mayor in", "is the", "one to, done"]) would be 3.