Test Your Knowledge: Answers

 

 
  1. You can use multiple-target assignments (A = B = C = 0), sequence assignment (A, B, C = 0, 0, 0), or multiple assignment statements on three separate lines (A = 0, B = 0, and C = 0). With the latter technique, as introduced in Chapter 10, you can also string the three separate statements together on the same line by separating them with semicolons (A = 0; B = 0; C = 0).
  2. If you assign them this way:

    A = B = C = []

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    all three names reference the same object, so changing it in-place from one (e.g., A.append(99)) will affect the others. This is true only for in-place changes to mutable objects like lists and dictionaries; for immutable objects such as numbers and strings, this issue is irrelevant.
  3. The list sort method is like append in that it makes an in-place change to the subject list—it returns None, not the list it changes. The assignment back to L sets L to None, not to the sorted list. As we’ll see later in this part of the book, a newer built-in function, sorted, sorts any sequence and returns a new list with the sorting result; because this is not an in-place change, its result can be meaningfully assigned to a name.
  4. To print to a file for a single print operation, you can use 3.0’s print(X, file=F) call form, use 2.6’s extended print >> file, X statement form, or assign sys.stdout to a manually opened file before the print and restore the original after. You can also redirect all of a program’s printed text to a file with special syntax in the system shell, but this is outside Python’s scope.