What does a beginning 'u do when defining a string in python?

Question

I just started learning python a few days ago and I came across the str.isdecimal() function. I get an error when I type the following into a python environment:

    text="123"
    Print text.isdecimal()

The error is: 'str' object has no attribute 'isdecimal'.

However, when I type the following:

    text=u"123"
    Print text.isdecimal()

Then things work out fine and I get "True" in return as expected.

My question

What is happening here? Specifically, what is the u doing to the string definition and why wont the isdecimal function work otherwise?

Thank you and sorry for if the question is too elementary.

Answer 1

isdecimal is a method on Unicode strings, but not byte strings. u'xxx' defines a Unicode string.

Answer 2

It defines the string as the unicode type, rather than a str type.

    type(u'foo')
    <type 'unicode'>