Python Multi-argument Function Call

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Из курса от партнера University of Alberta

Problem Solving, Programming, and Video Games

3 оценки

University of Alberta

Problem Solving, Programming, and Video Games

3 оценки

This course is an introduction to computer science and programming in Python. Upon successful completion of this course, you will be able to: 1. Take a new computational problem and develop a plan to solve it through problem understanding and decomposition. 2. Follow a design creation process that includes specifications, algorithms, and testing. 3. Code, test, and debug a program in Python, based on your design. Important computer science concepts such as problem solving (computational thinking), problem decomposition, algorithms, abstraction, and software quality are emphasized throughout. The Python programming language and video games are used to demonstrate computer science concepts in a concrete and fun manner. However, a learner can take the knowledge and skills from this course and apply them to non-game problems, other programming languages, and other computer science courses. You do not need any previous programming, Python, or video game experience. However, some computer skills (e.g., mouse, keyboard, document editing), knowledge of algebra, attention to detail (as with many technical subjects), and a “just give it a try” spirit will be keys to your success. Despite the use of video games for all the programming examples, PVG is not about computer games. PVG will still provide valuable knowledge and skills for non-game computational problems. The interactive learning objects (ILO) of the course provide automatic, context-specific guidance and feedback, like a virtual teaching assistant, as you develop problem descriptions, algorithms, and functional test plans. The course forums will be supported by the creators of the course, to help you succeed. All videos, assessments, and ILOs are available free of charge. There is an optional certificate available for a fee.

Из урока

Module 3: Hacking Version 2

In Module 3, you will identify solution issues in your game. You will apply a second form of the abstraction problem-solving technique, called using templates, to solve a solution issue by using a graphics library. You will then use lexics, syntax, and semantics to learn two new Python statements (assignment, import), two new Python expressions (binary expression, attribute reference), and one new Python type (module). You will employ these Python constructs and a simple graphics library to write, test, and debug Hacking Version 2.

Python Multi-argument Function Call5:23

Познакомьтесь с преподавателями

Duane Szafron
Professor
Computing Science
Paul Lu
Professor
Computing Science

[MUSIC]

In this video, we generalize the syntax and semantics of the function call

expression to support multiple arguments instead of zero or one argument.

Here is the current syntax for a function call with zero or

one argument that you have already seen.

Different functions actually support different numbers of arguments.

For example, the len function has exactly one argument.

The function randint,

from the random module in the standard library has two arguments.

This function returns a random number between its two argument objects.

Many Python functions can accept a variable number of arguments.

For example,

when the print function is called with no arguments, it displays a blank line.

When the print function is called with more than argument,

it evaluates its argument expressions and

displays all the result objects on one line separated by single blanks.

Here's the documentation for the built-in print function.

The symbol star before the first argument, objects, indicates that this function

accepts any number of arguments, zero or more, at this argument position.

That is why I could successfully call print with one argument, no arguments,

or three arguments.

We will ignore the rest of the print function argument documentation

until a future lesson.

I will generalize the function calls syntax to support more than one argument.

Here is a simplified syntax diagram for

the nonterminal argumentless state that supports one or more argument expressions.

I will use these syntax diagrams to show that print of 27, hello,

and 4 has valid syntax.

There are eight tokens in this line.

From the start state, the identifier token print matches the identifier state.

The left paren delimiter token matches the left paren state.

The next state is the nonterminal state, argument list.

Expand this nonterminal state to reveal the expression state.

Expand the expression state to reveal its literal, identifier, function call, and

binary expression states.

The literal integer token, 27, matches the literal accepting state so

the expression is valid.

The next taken is the comma delimiter which matches the comma state.

The next token is the literal string token, hello.

Expanding the expression state again reveals its internal states, and

hello matches the literal state, so this expression is valid.

The next token is the comma delimiter, which matches the comma state.

The next token is the integer literal four.

Expanding the expression state again finds a match with the literal state, so

the expression is valid.

The next token is the right paren delimiter token.

So the interpreter does not want to match any more expressions.

Since the current expression state is an accepting state

in the argument list nonterminal state, argument list is valid.

Returning to this syntax diagram for function call,

the right paren token matches the right paren state.

There are no more tokens.

Since the current state is an accepting state for

the function call, the function call is valid.

Since function call is in accepting state in the expression syntax diagram,

the entire expression has valid syntax.

Since the syntax is valid, the interpreter can apply semantic analysis.

Here is the previous semantic rule for

evaluating a function call with zero or one arguments.

I will modify this semantic rule to support multiple arguments.

Step one is the same.

Step two becomes, if there is an argument list,

evaluate it to obtain an argument object list.

Otherwise, create an empty argument object list.

Step three becomes, pass the argument object list to the function.

Step four is the same.

The semantics of the nonterminal argument list state are,

evaluate each expression from left to right and

add the result objects to an argument object list in order.

Let's apply these semantic rules to the multi-argument print function call.

When the program starts, the name print is pre-bound to the print function object.

Step one uses the semantics of identifier to de-reference print

in the program's name space to obtain the print function object.

Step two checks if there's an argument list.

Since there is an argument list between the parentheses,

the interpreter applies the semantics of an argument list.

Evaluate each of the three argument expressions using the semantics of

literals.

Then add each result object to the argument object list.

It will contain three objects, integer 27, string hello, and integer 4.

Step three passes this list of three object to the print function object.

Recall that a function is like a box with an argument object as input and

a result object as output.

The input is actually a list that contains zero or more argument objects.

Step four evaluates the print function object to display the three argument

objects, 27, hello, and 4 in human readable form, each separated by a blank.

The print function returns an object whose type is NoneType, and

this object is ignored.

In this video, we generalize the syntax and

semantics of function calls to support multiple arguments.

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