[PPT] - 61A Lecture 3 Wednesday, August 31 Life Cycle of a User-Defined PowerPoint Presentation

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61A Lecture 3

Wednesday, August 31

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Life Cycle of a User-Defined Function

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Def statement: Call expression: square( x ): return mul(x, x) >>> def square(2+2) Calling/Applying: square( x ): return mul(x, x) What happens?

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Life Cycle of a User-Defined Function

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Def statement: Call expression: square( x ): return mul(x, x) >>> def square(2+2) Calling/Applying: square( x ): return mul(x, x) D e f s t a t e m e n t What happens?

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Life Cycle of a User-Defined Function

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Def statement: Call expression: square( x ): return mul(x, x) >>> def square(2+2) Calling/Applying: square( x ): return mul(x, x) D e f s t a t e m e n t Formal parameter What happens?

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Life Cycle of a User-Defined Function

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Def statement: Call expression: square( x ): return mul(x, x) >>> def square(2+2) Calling/Applying: square( x ): return mul(x, x) D e f s t a t e m e n t Formal parameter B

d

y What happens?

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Life Cycle of a User-Defined Function

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Def statement: Call expression: square( x ): return mul(x, x) >>> def square(2+2) Calling/Applying: square( x ): return mul(x, x) D e f s t a t e m e n t Formal parameter B

d

y (return statement) What happens?

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Life Cycle of a User-Defined Function

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Def statement: Call expression: square( x ): return mul(x, x) >>> def square(2+2) Calling/Applying: square( x ): return mul(x, x) D e f s t a t e m e n t Formal parameter B

d

y R e t u r n e x p r e s s i

n

(return statement) What happens?

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Life Cycle of a User-Defined Function

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Def statement: Call expression: square( x ): return mul(x, x) >>> def square(2+2) Calling/Applying: square( x ): return mul(x, x) D e f s t a t e m e n t Formal parameter B

d

y R e t u r n e x p r e s s i

n

(return statement) Function created What happens?

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Life Cycle of a User-Defined Function

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Def statement: Call expression: square( x ): return mul(x, x) >>> def square(2+2) Calling/Applying: square( x ): return mul(x, x) D e f s t a t e m e n t Formal parameter B

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y R e t u r n e x p r e s s i

n

(return statement) Function created Name bound What happens?

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Life Cycle of a User-Defined Function

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Def statement: Call expression: square( x ): return mul(x, x) >>> def square(2+2) Calling/Applying: square( x ): return mul(x, x) D e f s t a t e m e n t Formal parameter B

d

y R e t u r n e x p r e s s i

n

(return statement) Function created Name bound

perand: 2+2

argument: 4 What happens?

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Life Cycle of a User-Defined Function

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Def statement: Call expression: square( x ): return mul(x, x) >>> def square(2+2) Calling/Applying: square( x ): return mul(x, x) D e f s t a t e m e n t Formal parameter B

d

y R e t u r n e x p r e s s i

n

(return statement) Function created Name bound

perand: 2+2

argument: 4 What happens?

perator: square

function: square

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Life Cycle of a User-Defined Function

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Def statement: Call expression: square( x ): return mul(x, x) >>> def square(2+2) Calling/Applying: square( x ): return mul(x, x) D e f s t a t e m e n t Formal parameter B

d

y R e t u r n e x p r e s s i

n

(return statement) Function created Name bound

perand: 2+2

argument: 4 Op's evaluated What happens?

perator: square

function: square

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Life Cycle of a User-Defined Function

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Def statement: Call expression: square( x ): return mul(x, x) >>> def square(2+2) Calling/Applying: square( x ): return mul(x, x) D e f s t a t e m e n t Formal parameter B

d

y R e t u r n e x p r e s s i

n

(return statement) Function created Name bound

perand: 2+2

argument: 4 Op's evaluated Function called with argument(s) What happens?

perator: square

function: square

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Life Cycle of a User-Defined Function

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Def statement: Call expression: square( x ): return mul(x, x) >>> def square(2+2) Calling/Applying: square( x ): return mul(x, x) D e f s t a t e m e n t Formal parameter B

d

y R e t u r n e x p r e s s i

n

(return statement) Function created Name bound

perand: 2+2

argument: 4 Op's evaluated Function called with argument(s) What happens?

perator: square

function: square Signature

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Life Cycle of a User-Defined Function

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Def statement: Call expression: square( x ): return mul(x, x) >>> def square(2+2) Calling/Applying: square( x ): return mul(x, x) D e f s t a t e m e n t Formal parameter B

d

y R e t u r n e x p r e s s i

n

(return statement) Function created Name bound

perand: 2+2

argument: 4 Op's evaluated Function called with argument(s) What happens?

perator: square

function: square Signature 4

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Life Cycle of a User-Defined Function

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Def statement: Call expression: square( x ): return mul(x, x) >>> def square(2+2) Calling/Applying: square( x ): return mul(x, x) D e f s t a t e m e n t Formal parameter B

d

y R e t u r n e x p r e s s i

n

(return statement) Function created Name bound

perand: 2+2

argument: 4 Op's evaluated Function called with argument(s) What happens?

perator: square

function: square Signature 4 16

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Life Cycle of a User-Defined Function

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Def statement: Call expression: square( x ): return mul(x, x) >>> def square(2+2) Calling/Applying: square( x ): return mul(x, x) D e f s t a t e m e n t Formal parameter B

d

y R e t u r n e x p r e s s i

n

(return statement) Function created Name bound

perand: 2+2

argument: 4 Op's evaluated Function called with argument(s) What happens?

perator: square

function: square Signature 4 16 Argument

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Life Cycle of a User-Defined Function

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Def statement: Call expression: square( x ): return mul(x, x) >>> def square(2+2) Calling/Applying: square( x ): return mul(x, x) D e f s t a t e m e n t Formal parameter B

d

y R e t u r n e x p r e s s i

n

(return statement) Function created Name bound

perand: 2+2

argument: 4 Op's evaluated Function called with argument(s) What happens?

perator: square

function: square Signature 4 16 Argument Return value

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Life Cycle of a User-Defined Function

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Def statement: Call expression: square( x ): return mul(x, x) >>> def square(2+2) Calling/Applying: square( x ): return mul(x, x) D e f s t a t e m e n t Formal parameter B

d

y R e t u r n e x p r e s s i

n

(return statement) Function created Name bound

perand: 2+2

argument: 4 Op's evaluated Function called with argument(s) What happens?

perator: square

function: square Signature 4 16 New frame! Argument Return value

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Life Cycle of a User-Defined Function

2

Def statement: Call expression: square( x ): return mul(x, x) >>> def square(2+2) Calling/Applying: square( x ): return mul(x, x) D e f s t a t e m e n t Formal parameter B

d

y R e t u r n e x p r e s s i

n

(return statement) Function created Name bound

perand: 2+2

argument: 4 Op's evaluated Function called with argument(s) What happens?

perator: square

function: square Signature 4 16 New frame! Params bound Argument Return value

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Life Cycle of a User-Defined Function

2

Def statement: Call expression: square( x ): return mul(x, x) >>> def square(2+2) Calling/Applying: square( x ): return mul(x, x) D e f s t a t e m e n t Formal parameter B

d

y R e t u r n e x p r e s s i

n

(return statement) Function created Name bound

perand: 2+2

argument: 4 Op's evaluated Function called with argument(s) What happens?

perator: square

function: square Signature 4 16 New frame! Params bound Body executed Argument Return value

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Life Cycle of a User-Defined Function

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Def statement: Call expression: square( x ): return mul(x, x) >>> def square(2+2) Calling/Applying: square( x ): return mul(x, x) D e f s t a t e m e n t Formal parameter B

d

y R e t u r n e x p r e s s i

n

(return statement) Function created Name bound

perand: 2+2

argument: 4 Op's evaluated Function called with argument(s) What happens?

perator: square

function: square Signature 4 16 New frame! Params bound Body executed Argument Return value N a m e

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Multiple Environments in One Diagram!

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Example: http://goo.gl/668fU

square(square(3)) square(3) 9 3 square square

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Multiple Environments in One Diagram!

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Example: http://goo.gl/668fU

27 square(square(3)) square(3) 9 3 square square An environment is a sequence of frames.

1 2 1 2 1

The global frame alone
A local, then the global frame

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Names Have No Meaning Without Environments

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Example: http://goo.gl/668fU

1 2 2 1 1

Every expression is evaluated in the context of an environment. A name evaluates to the value bound to that name in the earliest frame of the current environment in which that name is found. mul(x, x) “ m u l ” i s n

t

f

u

n d

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Formal Parameters

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Example: http://goo.gl/OapJa

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Formal Parameters

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def square(x): return mul(x, x)

Example: http://goo.gl/OapJa

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Formal Parameters

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def square(x): return mul(x, x) vs

Example: http://goo.gl/OapJa

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Formal Parameters

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def square(x): return mul(x, x) def square(y): return mul(y, y) vs

Example: http://goo.gl/OapJa

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Formal Parameters

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def square(x): return mul(x, x) def square(y): return mul(y, y) vs

Example: http://goo.gl/OapJa

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Formal Parameters

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def square(x): return mul(x, x) def square(y): return mul(y, y) vs

Example: http://goo.gl/OapJa

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Formal Parameters

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def square(x): return mul(x, x) def square(y): return mul(y, y) vs Formal parameters have local scope

Example: http://goo.gl/OapJa

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Formal Parameters

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def square(x): return mul(x, x) def square(y): return mul(y, y) vs Formal parameters have local scope (Demo)

Example: http://goo.gl/OapJa

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Python Feature Demonstration

<Demo> Operators Multiple Return Values Docstrings Doctests Default Arguments Statements </Demo>

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Statements

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A statement is executed by the interpret to perform an action

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<header>: <statement> <statement> ... <separating header>: <statement> <statement> ... ... Compound statements:

Statements

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A statement is executed by the interpret to perform an action

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<header>: <statement> <statement> ... <separating header>: <statement> <statement> ... ... Compound statements:

Statements

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A statement is executed by the interpret to perform an action Statement

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<header>: <statement> <statement> ... <separating header>: <statement> <statement> ... ... Compound statements:

Statements

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A statement is executed by the interpret to perform an action Statement Clause

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<header>: <statement> <statement> ... <separating header>: <statement> <statement> ... ... Compound statements:

Statements

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A statement is executed by the interpret to perform an action Statement Suite Clause

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<header>: <statement> <statement> ... <separating header>: <statement> <statement> ... ... Compound statements:

Statements

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A statement is executed by the interpret to perform an action Statement Suite Clause The first header determines a statement’s type

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<header>: <statement> <statement> ... <separating header>: <statement> <statement> ... ... Compound statements:

Statements

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A statement is executed by the interpret to perform an action Statement Suite Clause The first header determines a statement’s type The header of a clause “controls” the suite that follows

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<header>: <statement> <statement> ... <separating header>: <statement> <statement> ... ... Compound statements:

Statements

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A statement is executed by the interpret to perform an action Statement Suite Clause The first header determines a statement’s type The header of a clause “controls” the suite that follows def statements are compound statements

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Compound Statements

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Compound statements: <header>: <statement> <statement> ... <separating header>: <statement> <statement> ... ... Suite

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Compound Statements

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Compound statements: <header>: <statement> <statement> ... <separating header>: <statement> <statement> ... ... Suite A suite is a sequence

f statements

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Compound Statements

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Compound statements: <header>: <statement> <statement> ... <separating header>: <statement> <statement> ... ... Suite A suite is a sequence

f statements

To “execute” a suite means to execute its sequence of statements, in order

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Compound Statements

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Compound statements: <header>: <statement> <statement> ... <separating header>: <statement> <statement> ... ... Execution Rule for a sequence of statements:

Execute the first
Unless directed otherwise, execute the rest

Suite A suite is a sequence

f statements

To “execute” a suite means to execute its sequence of statements, in order

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Local Assignment

def percent_difference(x, y): difference = abs(x-y) return 100 * difference / x percent_difference(40, 50)

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Local Assignment

def percent_difference(x, y): difference = abs(x-y) return 100 * difference / x percent_difference(40, 50)

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Conditional Statements

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def absolute_value(x): """Return the absolute value of x.""" if x > 0: return x elif x == 0: return 0 else: return -x

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Conditional Statements

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def absolute_value(x): """Return the absolute value of x.""" if x > 0: return x elif x == 0: return 0 else: return -x 1 statement, 3 clauses, 3 headers, 3 suites

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Conditional Statements

Execution rule for conditional statements:

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def absolute_value(x): """Return the absolute value of x.""" if x > 0: return x elif x == 0: return 0 else: return -x 1 statement, 3 clauses, 3 headers, 3 suites

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Conditional Statements

Execution rule for conditional statements:

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def absolute_value(x): """Return the absolute value of x.""" if x > 0: return x elif x == 0: return 0 else: return -x 1 statement, 3 clauses, 3 headers, 3 suites Each clause is considered in order.

1. Evaluate the header's expression.
2. If it is a true value, execute the suite & skip the rest.

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Boolean Contexts

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def absolute_value(x): """Return the absolute value of x.""" if x > 0: return x elif x == 0: return 0 else: return -x

George Boole

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Boolean Contexts

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def absolute_value(x): """Return the absolute value of x.""" if x > 0: return x elif x == 0: return 0 else: return -x

George Boole

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Boolean Contexts

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def absolute_value(x): """Return the absolute value of x.""" if x > 0: return x elif x == 0: return 0 else: return -x Two boolean contexts

George Boole

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Boolean Contexts

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def absolute_value(x): """Return the absolute value of x.""" if x > 0: return x elif x == 0: return 0 else: return -x Two boolean contexts

George Boole

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Boolean Contexts

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def absolute_value(x): """Return the absolute value of x.""" if x > 0: return x elif x == 0: return 0 else: return -x Two boolean contexts

George Boole

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Boolean Contexts

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def absolute_value(x): """Return the absolute value of x.""" if x > 0: return x elif x == 0: return 0 else: return -x Two boolean contexts False values in Python: False, 0, '', None

George Boole

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Boolean Contexts

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def absolute_value(x): """Return the absolute value of x.""" if x > 0: return x elif x == 0: return 0 else: return -x Two boolean contexts False values in Python: False, 0, '', None (more to come)

George Boole

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Boolean Contexts

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def absolute_value(x): """Return the absolute value of x.""" if x > 0: return x elif x == 0: return 0 else: return -x Two boolean contexts False values in Python: False, 0, '', None True values in Python: Anything else (True) (more to come)

George Boole

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Boolean Contexts

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def absolute_value(x): """Return the absolute value of x.""" if x > 0: return x elif x == 0: return 0 else: return -x Two boolean contexts False values in Python: False, 0, '', None True values in Python: Anything else (True) (more to come)

George Boole

Read Section 1.5.4!

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Iteration

14

1. Evaluate the header’s expression.
2. If it is a true value,

execute the (whole) suite, then return to step 1. Execution rule for while statements: i, total = 0, 0 while i < 3: i = i + 1 total = total + i 1 2 3 6

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Iteration

14

1. Evaluate the header’s expression.
2. If it is a true value,

execute the (whole) suite, then return to step 1. Execution rule for while statements: i, total = 0, 0 while i < 3: i = i + 1 total = total + i 1 2 3 6

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Iteration

14

1. Evaluate the header’s expression.
2. If it is a true value,

execute the (whole) suite, then return to step 1. Execution rule for while statements: i, total = 0, 0 while i < 3: i = i + 1 total = total + i 1 2 3 6

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Iteration

14

1. Evaluate the header’s expression.
2. If it is a true value,

execute the (whole) suite, then return to step 1. Execution rule for while statements: i, total = 0, 0 while i < 3: i = i + 1 total = total + i i: total: 1 2 3 6

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Iteration

14

1. Evaluate the header’s expression.
2. If it is a true value,

execute the (whole) suite, then return to step 1. Execution rule for while statements: i, total = 0, 0 while i < 3: i = i + 1 total = total + i i: total: 1 2 3 6

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Iteration

14

1. Evaluate the header’s expression.
2. If it is a true value,

execute the (whole) suite, then return to step 1. Execution rule for while statements: i, total = 0, 0 while i < 3: i = i + 1 total = total + i i: total: 1 2 3 6

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Iteration

14

1. Evaluate the header’s expression.
2. If it is a true value,

execute the (whole) suite, then return to step 1. Execution rule for while statements: i, total = 0, 0 while i < 3: i = i + 1 total = total + i i: total: 1 2 3 6

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Iteration

14

1. Evaluate the header’s expression.
2. If it is a true value,

execute the (whole) suite, then return to step 1. Execution rule for while statements: i, total = 0, 0 while i < 3: i = i + 1 total = total + i i: total: 1 2 3 6

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Iteration

14

1. Evaluate the header’s expression.
2. If it is a true value,

execute the (whole) suite, then return to step 1. Execution rule for while statements: i, total = 0, 0 while i < 3: i = i + 1 total = total + i i: total: 1 2 3 6

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Iteration

14

1. Evaluate the header’s expression.
2. If it is a true value,

execute the (whole) suite, then return to step 1. Execution rule for while statements: i, total = 0, 0 while i < 3: i = i + 1 total = total + i i: total: 1 2 3 6

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Iteration

14

1. Evaluate the header’s expression.
2. If it is a true value,

execute the (whole) suite, then return to step 1. Execution rule for while statements: i, total = 0, 0 while i < 3: i = i + 1 total = total + i i: total: 1 2 3 6

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Iteration

14

1. Evaluate the header’s expression.
2. If it is a true value,

execute the (whole) suite, then return to step 1. Execution rule for while statements: i, total = 0, 0 while i < 3: i = i + 1 total = total + i i: total: 1 2 3 6

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Iteration

14

1. Evaluate the header’s expression.
2. If it is a true value,

execute the (whole) suite, then return to step 1. Execution rule for while statements: i, total = 0, 0 while i < 3: i = i + 1 total = total + i i: total: 1 2 3 6

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Iteration

14

1. Evaluate the header’s expression.
2. If it is a true value,

execute the (whole) suite, then return to step 1. Execution rule for while statements: i, total = 0, 0 while i < 3: i = i + 1 total = total + i i: total: 1 2 3 6

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Iteration

14

1. Evaluate the header’s expression.
2. If it is a true value,

execute the (whole) suite, then return to step 1. Execution rule for while statements: i, total = 0, 0 while i < 3: i = i + 1 total = total + i i: total: 1 2 3 6

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Iteration

14

1. Evaluate the header’s expression.
2. If it is a true value,

execute the (whole) suite, then return to step 1. Execution rule for while statements: i, total = 0, 0 while i < 3: i = i + 1 total = total + i i: total: 1 2 3 6

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Iteration

14

1. Evaluate the header’s expression.
2. If it is a true value,

execute the (whole) suite, then return to step 1. Execution rule for while statements: i, total = 0, 0 while i < 3: i = i + 1 total = total + i i: total: 1 2 3 6

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Iteration

14

1. Evaluate the header’s expression.
2. If it is a true value,

execute the (whole) suite, then return to step 1. Execution rule for while statements: i, total = 0, 0 while i < 3: i = i + 1 total = total + i i: total: 1 2 3 6

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Iteration

14

1. Evaluate the header’s expression.
2. If it is a true value,

execute the (whole) suite, then return to step 1. Execution rule for while statements: i, total = 0, 0 while i < 3: i = i + 1 total = total + i i: total: 1 2 3 6

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Iteration

14

1. Evaluate the header’s expression.
2. If it is a true value,

execute the (whole) suite, then return to step 1. Execution rule for while statements: i, total = 0, 0 while i < 3: i = i + 1 total = total + i i: total: 1 2 3 6

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Iteration

14

1. Evaluate the header’s expression.
2. If it is a true value,

execute the (whole) suite, then return to step 1. Execution rule for while statements: i, total = 0, 0 while i < 3: i = i + 1 total = total + i i: total: 1 2 3 6

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The Fibonacci Sequence

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The Fibonacci Sequence

15

0, 1, 1, 2, 3, 5, 8, 13, ...

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The Fibonacci Sequence

def fib(n): """Compute the nth Fibonacci number, for n >= 2.""" pred, curr = 0, 1 # First two Fibonacci numbers k = 2 # Tracks which Fib number is curr while k < n: pred, curr = curr, pred + curr k = k + 1 return curr

15

0, 1, 1, 2, 3, 5, 8, 13, ...

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pred: curr: ...

The Fibonacci Sequence

def fib(n): """Compute the nth Fibonacci number, for n >= 2.""" pred, curr = 0, 1 # First two Fibonacci numbers k = 2 # Tracks which Fib number is curr while k < n: pred, curr = curr, pred + curr k = k + 1 return curr

15

0, 1, 1, 2, 3, 5, 8, 13, ...

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pred: curr: ...

The Fibonacci Sequence

def fib(n): """Compute the nth Fibonacci number, for n >= 2.""" pred, curr = 0, 1 # First two Fibonacci numbers k = 2 # Tracks which Fib number is curr while k < n: pred, curr = curr, pred + curr k = k + 1 return curr

15

0, 1, 1, 2, 3, 5, 8, 13, ...

SLIDE 88

pred: curr: ...

The Fibonacci Sequence

def fib(n): """Compute the nth Fibonacci number, for n >= 2.""" pred, curr = 0, 1 # First two Fibonacci numbers k = 2 # Tracks which Fib number is curr while k < n: pred, curr = curr, pred + curr k = k + 1 return curr

15

0, 1, 1, 2, 3, 5, 8, 13, ...

SLIDE 89

pred: curr: ...

The Fibonacci Sequence

def fib(n): """Compute the nth Fibonacci number, for n >= 2.""" pred, curr = 0, 1 # First two Fibonacci numbers k = 2 # Tracks which Fib number is curr while k < n: pred, curr = curr, pred + curr k = k + 1 return curr

15

0, 1, 1, 2, 3, 5, 8, 13, ...

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pred: curr: ...

The Fibonacci Sequence

def fib(n): """Compute the nth Fibonacci number, for n >= 2.""" pred, curr = 0, 1 # First two Fibonacci numbers k = 2 # Tracks which Fib number is curr while k < n: pred, curr = curr, pred + curr k = k + 1 return curr

15

0, 1, 1, 2, 3, 5, 8, 13, ...

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pred: curr: ...

The Fibonacci Sequence

def fib(n): """Compute the nth Fibonacci number, for n >= 2.""" pred, curr = 0, 1 # First two Fibonacci numbers k = 2 # Tracks which Fib number is curr while k < n: pred, curr = curr, pred + curr k = k + 1 return curr

15

0, 1, 1, 2, 3, 5, 8, 13, ...

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pred: curr: ...

The Fibonacci Sequence

def fib(n): """Compute the nth Fibonacci number, for n >= 2.""" pred, curr = 0, 1 # First two Fibonacci numbers k = 2 # Tracks which Fib number is curr while k < n: pred, curr = curr, pred + curr k = k + 1 return curr

15

0, 1, 1, 2, 3, 5, 8, 13, ...

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Project 1: Hog

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