Example 1:

mylist = ['a','b','c','d','e']
mylist.insert(len(mylist),'f')
print(mylist)

Output: ['a', 'b', 'c', 'd', 'e', 'f']

Example 2:

mylist = ['a','b','c','d','e']
mylist.insert(10,'f')
print(mylist)

Output: ['a', 'b', 'c', 'd', 'e', 'f']

Why should mylist.insert(len(mylist), x) be equivalent to mylist.insert(len(mylist)+1000000000, x)

Excepted Output: Should give index error.

The docs say that:
  l.insert(pos, val)
is equivalent to:
  l[pos:pos] = [val]
The docstring also says that the value is inserted before pos, so .insert is working as documented.