Python Multi-argument Function Call

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Из курса от партнера University of Alberta

Problem Solving, Programming, and Video Games

6 оценки

University of Alberta

Problem Solving, Programming, and Video Games

6 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 Call5:22

Познакомьтесь с преподавателями

Duane Szafron
Professor
Computing Science
Paul Lu
Professor
Computing Science

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 one argument,

it evaluates its argument expressions and displays

all the results 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 co-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 call syntax to support more than one argument.

Here is a simplified syntax diagram for

the non-terminal argument list state that supports one or more argument expressions.

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

hello, and four, has valid syntax.

There are eight tokens in this line.

From the start state,

the identifier token print matches the identifier state.

The left parenth delimiter token matches the left parenth state.

The next state is the non-terminal state argument list.

Expand this non terminal 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 token 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 parenth delimiter token,

so the interpreter does not want to match anymore expressions.

Since the current expression state is

an accepting state in the argument list non-terminal state,

argument list is valid.

Returning to the syntax diagram for function call,

the right parenth token matches the right parenth 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 an 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 role 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 non-terminal argument list state R,

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-round to the print function object.

Step one uses the semantics of identifier to

dereference print in the program's namespace to obtain the print function object.

Step two checks if there is 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 four.

Step three passes this list of three objects 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 four 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 generalized the syntax and semantics of

function calls to support multiple arguments.

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