1 00:00:05,160 --> 00:00:07,960 In this section, you've learnt a lot about functions. 2 00:00:07,960 --> 00:00:11,620 Not everything yet, but enough to let you write our own functions. 3 00:00:11,620 --> 00:00:16,790 You now understand what parameters and arguments are, and how the arguments provide the values 4 00:00:16,790 --> 00:00:18,560 for your formal parameters. 5 00:00:18,560 --> 00:00:22,470 You define and name your parameters when you define the function. 6 00:00:22,470 --> 00:00:24,760 You then pass arguments when you call the function. 7 00:00:24,760 --> 00:00:30,710 You've seen how the flow of execution jumps into the function body, when a function is 8 00:00:30,710 --> 00:00:34,980 called, and returns to the calling code, when the function terminates. 9 00:00:34,980 --> 00:00:42,440 We covered scope, and saw that our parameter variables only exist inside the function. 10 00:00:42,440 --> 00:00:44,940 They're not available in the code outside the function. 11 00:00:44,940 --> 00:00:50,850 We still have a bit more to learn about scope, but we know all we need to write our own functions. 12 00:00:50,850 --> 00:00:55,649 We looked at functions that perform actions, and functions that return a result. 13 00:00:55,649 --> 00:01:00,840 It is possible for a function to do both, but we haven't seen any examples of that. 14 00:01:00,840 --> 00:01:06,460 We deliberately didn't write functions that way, because you should generally avoid doing it 15 00:01:06,460 --> 00:01:11,360 Functions should be self contained blocks of code, that either perform some action, 16 00:01:11,360 --> 00:01:12,830 or return a result. 17 00:01:12,830 --> 00:01:17,660 Doing both in the same function can result in code that's difficult to maintain. 18 00:01:17,660 --> 00:01:21,800 Functions that perform an action used to be called procedures, but modern programming 19 00:01:21,800 --> 00:01:23,490 languages no longer make that distinction. 20 00:01:23,490 --> 00:01:26,890 Instead, they return None, in Python. 21 00:01:26,890 --> 00:01:32,640 Languages like C and Java use void as the return type, to indicate that nothing is returned. 22 00:01:32,640 --> 00:01:38,360 We've seen how to provide default values for our parameters. 23 00:01:38,360 --> 00:01:43,080 Default values make using the function easier, because you don't have to provide arguments 24 00:01:43,080 --> 00:01:46,060 for commonly used parameter values. 25 00:01:46,060 --> 00:01:51,130 We used the parameter name, when specifying an argument, in the banner_text function. 26 00:01:51,130 --> 00:01:56,800 Keyword arguments let you pass arguments in a different order than the parameters are defined. 27 00:01:56,800 --> 00:02:01,130 More importantly, they allow arguments to be provided, when a parameter with a default 28 00:02:01,130 --> 00:02:03,670 value appears earlier in the list. 29 00:02:03,670 --> 00:02:10,720 We saw one example of that, when we wanted to change the screen_width without providing any text. 30 00:02:10,720 --> 00:02:14,050 Docstrings are an important feature of Python functions. 31 00:02:14,050 --> 00:02:18,190 They're used to document what the function does, and how to use it. 32 00:02:18,190 --> 00:02:22,220 You've had a lot of practice writing Docstrings, and will get more as you write more functions 33 00:02:22,220 --> 00:02:24,360 in later sections. 34 00:02:24,360 --> 00:02:27,430 Function annotations also help with documenting your functions. 35 00:02:27,430 --> 00:02:31,200 They describe the type of the arguments, and the return value. 36 00:02:31,200 --> 00:02:36,850 Type hints perform a similar job, but are used for variables in your main program. 37 00:02:36,850 --> 00:02:40,980 A very important part of programming is testing. 38 00:02:40,980 --> 00:02:46,100 We learned how to activate a virtual environment, so that we could run our code like our users will run it. 39 00:02:46,100 --> 00:02:49,180 We also used a function to test the HiLo game. 40 00:02:49,180 --> 00:02:53,790 Putting the code into a function allowed us to test every possible value. 41 00:02:53,790 --> 00:02:56,090 That would be very tedious to do manually. 42 00:02:56,090 --> 00:03:01,430 We haven't looked at automated testing yet, but that example demonstrated how useful it can be. 43 00:03:01,430 --> 00:03:05,900 If we can get the computer to test our code, we can perform more thorough tests, and save 44 00:03:05,900 --> 00:03:08,350 ourselves a lot of time. 45 00:03:08,350 --> 00:03:13,420 We finished the section by looking at the 5 different types of parameters. 46 00:03:13,420 --> 00:03:18,100 We haven't discussed positional-only parameters, because you're unlikely to use them. 47 00:03:18,100 --> 00:03:22,760 var-keyword parameters will be discussed later, after you've learnt about Python dictionaries. 48 00:03:22,760 --> 00:03:27,830 We've seen examples of the other 3 parameter types, and used them in our functions. 49 00:03:27,830 --> 00:03:32,650 In the next section, we'll look at Python dictionaries and sets.