Test Your Knowledge: Answers

 

 
  1. The output here is 'Spam', because the function references a global variable in the enclosing module (because it is not assigned in the function, it is considered global).
  2. The output here is 'Spam' again because assigning the variable inside the function makes it a local and effectively hides the global of the same name. The print statement finds the variable unchanged in the global (module) scope.
  3. It prints 'NI' on one line and 'Spam' on another, because the reference to the variable within the function finds the assigned local and the reference in the print statement finds the global.
  4. This time it just prints 'NI' because the global declaration forces the variable assigned inside the function to refer to the variable in the enclosing global scope.
  5. The output in this case is again 'NI' on one line and 'Spam' on another, because the print statement in the nested function finds the name in the enclosing function’s local scope, and the print at the end finds the variable in the global scope.
  6. This example prints 'Spam', because the nonlocal statement (available in Python 3.0 but not 2.6) means that the assignment to X inside the nested function changes X in the enclosing function’s local scope. Without this statement, this assignment would classify X as local to the nested function, making it a different variable; the code would then print 'NI' instead.
  7. Although the values of local variables go away when a function returns, you can make a Python function retain state information by using shared global variables, enclosing function scope references within nested functions, or using default argument values. Function attributes can sometimes allow state to be attached to the function itself, instead of looked up in scopes. Another alternative, using OOP with classes, sometimes supports state retention better than any of the scope-based techniques because it makes it explicit with attribute assignments; we’ll explore this option in Part VI.