This page intentionally left blank Python for Software Design
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| return value: The result of a function. If a function call is used as an expression, the
return value is the value of the expression. stack diagram: A graphical representation of a stack of functions, their variables, and the values they refer to. traceback: A list of the functions that are executing, printed when an exception occurs. void function: A function that doesn’t return a value. 3.15 EXERCISES Exercise 3.3 Python provides a built-in function called len that returns the length of a string, so the value of len('allen') is 5. Write a function named right_justify that takes a string named s as a parameter and prints the string with enough leading spaces so that the last letter of the string is in column 70 of the display. >>> right_justify('allen') allen Exercise 3.4 A function object is a value you can assign to a variable or pass as an argument. For example, do_twice is a function that takes a function object as an argument and calls it twice: def do_twice(f): f() f() Here’s an example that uses do_twice to call a function named print_spam twice. def print_spam(): print 'spam' do_twice(print_spam) (1) Type this example into a script and test it. (2) Modify do_twice so that it takes two arguments, a function object and a value, and calls the function twice, passing the value as an argument. (3) Write a more general version of print_spam, called print_twice, that takes a string as a parameter and prints it twice. 34 Functions (4) Use the modified version of do_twice to call print_twice twice, passing 'spam' as an argument. (5) Define a new function called do_four that takes a function object and a value and calls the function four times, passing the value as a parameter. There should be only two statements in the body of this function, not four. You can see my solution at thinkpython.com/code/do_four.py. Exercise 3.5 This exercise † can be done using only the statements and other features we have learned so far. (1) Write a function that draws a grid like the following: + - - - - + - - - - + | | | | | | | | | | | | + - - - - + - - - - + | | | | | | | | | | | | + - - - - + - - - - + Hint: to print more than one value on a line, you can print a comma-separated sequence: print '+', '-' If the sequence ends with a comma, Python leaves the line unfinished, so the value printed next appears on the same line. print '+', print '-' The output of these statements is '+ -'. A print statement all by itself ends the current line and goes to the next line. (2) Use the previous function to draw a similar grid with four rows and four columns. You can see my solution at thinkpython.com/code/grid.py. † Based on an exercise in Oualline, Practical C Programming, Third Edition, O’Reilly (1997). |