Question

In the code below:

def modify_note(self):
    id = input("Enter a note id: ")
    memo = input("Enter a memo: ")
    tags = input("Enter tags: ")
    if memo:
       self.notebook.modify_memo(id, memo)
    if tags:
       self.notebook.modify_tags(id, tags)

memo and tags are string type variables. How can you write them after if, does python regard them as boolean here?

Answer 1

The if memo and if tags statements are checking the truthiness of the memo and tags variables.

Any object can be tested for truth
value, for use in an if or while
condition or as operand of the Boolean
operations below. The following values
are considered false:

• None
• False
• zero of any numeric type, for example, 0, 0L, 0.0, 0j.
• any empty sequence, for example, '', (), [].
• any empty mapping, for example, {}.
• instances of user-defined classes, if the class defines a __nonzero__()
  or __len__() method, when that
  method returns the integer zero or
  bool value False.

All other values are considered true —
so objects of many types are always
true.