COMP1021_HKUST@Spring2013

COMP1021: PYTHON SYNTAX BOX Contents Basic Syntax .................................................................................................................................................................................................................................................. 2 Modular programming ................................................................................................................................................................................................................................ 4 Advanced Syntax ........................................................................................................................................................................................................................................ 5 Python – Optimisation .................................................................................................................................................................................................................................. 7 Python – File Handling.................................................................................................................................................................................................................................. 7 Control Statements ...................................................................................................................................................................................................................................... 8 Turtle Functions – Import turtle .................................................................................................................................................................................................................... 8 Turtle Functions – Event Handling ............................................................................................................................................................................................................. 11 Time library – Managing python time ...................................................................................................................................................................................................... 12 Random Library – Import random ............................................................................................................................................................................................................ 12 (External Library) Music Functions – import pygame.midi..................................................................................................................................................................... 12 Initialisation and Closing ........................................................................................................................................................................................................................ 12 L-System (Start value, Replacement rules, …) ........................................................................................................................................................................................ 13 Appendix-Instrument ................................................................................................................................................................................................................................. 14

1

Basic Syntax I/O Functions Conversion Functions

print(‘’, end=’’)

Output a string on the screen (Default: end=eoln) end = End the line with escape char or other (e.g. eoln, null) Convert into

int()

str()

Convert any into

ord()

Return the ASCII code of the char in decimal number system Arithmetic Functions

= input(‘’)

Prompt a string  Input a string

round(, ) return

Round the into float number with If not set: Convert into integer If = 0, data type remains unchanged

max ()

chr()

Return the char with specified ordinal value

round(, ) return

Does nothing with even with greater than 0

max ()

Return the max value Return the min value If = : Ordinal value (e.g. ord(‘B’) > ord(‘A’) If … = : max() = max(.keys()), max(.items()) .keys() Return , Comments

‘’’ ‘’’

#

Comments in paragraph length Operators

Comments on a single line

// (Division  integer), % (Mod)

+= (a = a + …)

Truncated: 不要小數點後的字 (e.g.) 8.5 % 2 = 0.5 (Modulus operator: No conversion) >>> 2.0000000000000001 == 2 True >>> 2.000000000000001 == 2 False >>> type(2/2) >>> type(2//2)

Shorthand Assignment ( = )

Comparison Operator

==, !=, >=, , != == Comparison operator

True or || > 0 (Non-zero)

False or = 0

break Current

not and or Logical operator

continue

Loop Structure

Current Loop

Current Iteration

Loop Structure

Next Iteration

iteration

”continue” Statement of Current Loop Structure

Swapping

, , …= , , … Assign the nth value of the list on the right to the nth item of the list on the left ( s can be of different types

)

= [ : : -1] As = -1, not specified = -1, not specified = Error Reporting

Try

import sys #Recognise System Error

Process

cases

try:

Programme

except

except :

Exception

Error:



ValueError



I/O error

Datatype

Error

else: Reminder

Quotes in Python can be “ (Double quote) or ‘ (Single quote) They must be in pair Indentation  Indentation takes over any structural brackets  Indentation wrong  Syntax Error

All { (Big bracket) or ; (Semi-colon) Replaced by indentation in Python

Range 或 List 的 Step 定奪【沒提供】的 start or end 的 Value Positive Step: start = 0 , end = len() Negative Step: start = ord(last item), end =

Pressing

Kill the program in a friendly way

3

Modular programming Defining functions

def (, , …):

return Return a value and Variables:

Define your own function,

parameters

Procedure

Define Global vs. Local Class and objects

Define the Class Name. All included function can be called by .

def __init__ (self, , ):

Define the initial parameters that new class objects have to provide 1st self

def (self, , …) Functions

__init__

Variables

Local variable is limited to functions

class :

Class

Function

= ‘’

can be used outside modules

1st

Function

localized 的 Global Variable vs. Local variable

global

Define Function

end

self. =

self

variables

self.

Call

(@Class)

variables

= (, , …) Define new object as a member of the class

4

 

Instance Objects (Attribute Reference) (Class obj.) Method Objects ( )



Property (

)

Advanced Syntax Range (List) (Array)

range(, , )

list(range(0, 3)) == 0, 1, 2 3-1

A temporary list consisting integers from to Step: +1 +



range(, , )

range(, ) Range from to - 1

Range from large to small, with negative step [int_h]

(e.g. of ): ’funny’[-1:2:] == ‘’

[int_l-1]

[, , …]

e.g. p == ape[1] String is a list of characters

= [, ,…]

= (, ,…)

Items can be in different types Enclosed by a pair of square brackets Can be modified positive ordinal value: from 0 from left [0]: Leftmost item List (Functions)

’funny’[2:-1:] == ‘nn’

character == []

Self-defined set starting with item 0 (ordinal value == 0) List and tuple

‘funny’[-1:2:-1] == ‘yn’

Items can be in different types Enclosed by a pair of normal brackets Cannot be modified (Constant list) negative ordinal value: from -1 from right [-1]: Rightmost item

.insert(, )

.remove () Remove the from

String

Insert an into the of the

[::]

.append() Append an to the

: remains unchanged Output an modified with specified features

.index()

= .pop()

Return the position of the in the list

Remove the last item in the list and contain with 5

如果沒有的話，Return: “ is not in the list Dictionary = List type with (not only automatically assigned integer) (When calling them, the order of all items are rearranged)

Nested List (record) (3D structure) String Tuple List Tuple

Default = len() - 1

= { : , : , …}

for key, value in .items(): print(key, value)

[] =

Print out

()

.items()

.values()

dict_items([(, ), (, ), …])

dict_values([, , …]) Assessing Items

del []

.keys()

Delete the item (key and value) with del : Can be used for any :  Remove its memory location

dict_keys([, , , …]) 

[x_axis][y_axis][z_axis] Excel

Database

line by line



Record

2D Structure 3D Structure

Surface Cube

Datum Datum

[::]

len() Return the length of the list = ord([-1]) + 1

(e.g.) ‘funny’[1:3] == ‘un’ (Not ‘unn’ ) Default: == 0, == len(string_type>)，反正是最後 一個 char

char

+

*

copies of : 重複而已 (e.g.) ‘fun’ * 3 == ‘funfunfun’

Text concatenation: (e.g.) ‘fun’ + ‘kid’ == ‘funkid’

6

Python – Optimisation Turtle library

turtle.undo()

turtle.setundobuffer()

Undo the previous turtle process Improt sys

sys.getrecursionlimit()

can be

Return the size of the stack for python

None

:

undo buffer

sys.setrecursionlimit()

Set the size of the stack to Stack ……

Python – File Handling Escape characters Read & Write files

\t

Tab character

\n

New line character

= open(‘’, ‘r’) ‘r’: Open the file as Read-Only Mode

= open(‘’, ‘’) ‘w’: Open the file as Write Mode ‘wt’: Open the file using write + text mode Whenever the file is opened this way, everything in the file is cleared.

.write()

.close()

Write the to the : Will be in

_io.TextIOWrapper

for line in : .readlines() Remove char (String )

list

class (not str class)

statement

Lines



[] items

Default = space character .strip

.strip(‘’)

String

Free up System resources



.lstrip(‘’)



= .split(‘’)

Slice at all positions of  Create a

7

.rstrip(‘’))



Control Statements If Statement

if :

elif :

If condition if true, run the process

else:

一定要有 If Statemtn 在前（廢話）If … else if … else … While Loop

while : Condition == True,

For Loop

”break” or

condition == False

for in :

_

variable (e.g.) for _ in range(10):

Integer or character = List items,

List

ordinal item

Turtle Functions – Import turtle (usr_turtle:User-defined turtle)(turtle: System turtle, with all attributes accessible) Basic

Import turtle

Import the turtle library for use Movement

usr_turtle.goto(, )

usr_turtle.reset()

Initialise the turtle on the screen

usr_turtle.forward() Move the turtle ahead of its present direction

turtle.done()

Stop the turtle from further intruption

usr_turtle.backward()

Move the turtle back to the direction if its tail

usr_turtle.setpos(, )

Initial position (middle) = 0, 0 Move the turtle to a specific coordinate on the screen

usr_turtle.left()

Rotate the turtle leftward by degrees Drawing

usr_turtle.width()

usr_turtle.right()

Rotate the turtle rightward by degrees

usr_turtle.up() 8

usr_turtle.speed() 0: Instant ; 1: Slow < 10: Fast

usr_turtle.down()

Put down the turtle  Draw when moving

Set the width of lines drawn by turtle in pixels

Take up the turtle  Not drawing when moving

turtle.begin_fill()

usr_turtle.fillcolor()



Set fill colour in colour

turtle.end_fill()

Fill the shape drawn by the turtle with fill colour

usr_turtle.fillcolor()

usr_turtle.color() Set colour for both fill colour and pen colour

usr_turtle.color(, )

Return the present fill color

Set colour for 2 types of colours

usr_turtle.undo() Undo the previous step as stored in the turtle stack

usr_turtle.color() pen colour and fill colour

usr_turtle.dot(, )

usr_turtle.write(, align=””, font = (“”, “”)

Define the dot size and drop a dot Geometry

Write on with the 1st char of on turtle

usr_turtle.circle(, ) Draw a circle with radius specified and centre at from the left of the usr_turtle. : +ve: Centre on the left; -ve: Centre on the right Counterclockwise ( > 0) Draw with . A complete circle is 360

Turtle Screen Control

turtle.update() Update the turtle screen To be used after usr_turtle.tracer(False)

usr_turtle.clear()

usr_turtle.tracer(True):

turtle.bgcolor()

Set the background colour of turtle screen

usr_turtle.hideturtle()

Clear the drawings from , not other turtles

turtle.tracer () usr_turtle.tracer(False):

.

usr_turtle.showturtle() Turtle

turtle.colormode(1.0) 1.0

: Float type,

255

Set colour attributes into format

turtle.colormode(255)

: Integer Type

Set colour attributes into

0.0 ~ 1.0

Turtle name

Color attribute Assign

turtle.bgpic(‘’)

Set the background image to the 9

0 ~ 255 format Color

Turtle system settings

turtle.mode(‘world’) / turtle.mode(‘standard’)

Use the self-defined world or standard for turtle

turtle.setup(width=, height=)

Setup the turtle screen size. For , it means the % of the OS screen occupied by this turtle screen

turtle.setworldcoordinates(, , , )

Define the coordinates of the new world Recurring functions Define new turtles

turtle.ontimer(, )

Recur the function per infinitely

usr_turtle.shape (‘’)

Predefined shapes: Arrow, Turtle, Circle, Square, Triangle, Classic

turtle.addshape (‘’) User defined shape can be used only after addshape

usr_turtle.shapesize(‘’, ‘’) Define the turtle size with heights and width

= turtle.Turtle() Define new turtle with name =

= [] .append(turtle.Turtle())

Make good use of append(), instead of predefining the amount of list items (e.g.) turtles[i] = usr_turtle.Turtle()

10

Turtle Functions – Event Handling usr_turtle.on (Mouse movement) No brackets after (i.e. (),

usr_turtle.onclick ()

Run the when the turtle in clicked by mouse

usr_turtle.ondrag () Run the when users drags the turtle

Move the turtle according to your mouse movement For instant update of the position, need usr_turtle.tracer(False) + usr_turtle.update()

usr_turtle.xcor()

usr_turtle.ycor() Return the y coordinate of the turtle

turtle.onscreenclick ()

Run the when the screen is clicked by mouse

turtle.onkeypress (, ‘’)

turtle.onkeyrelease(, ‘’) Run the Run the when the is released

turtle.listen() Keep listening any keyboard event Run this like usr_turtle.done(), must-have +

Run the when the is pressed All turtle.on + Related to

Run the according to the timer

usr_turtle.ondrag (usr_turtle.goto)

Return the x coordinate of the turtle usr_turtle.on (KB, MOUSE, clicking)

turtle.ontimer (, )

: Requires def (null_x, null_y)

11

Program

Time library – Managing python time Time halt

Condition: Used for delay in pressing/ leaving on/from a note Smooth

time.sleep()

Wait for seconds to next statement Python uptime

time.clock()

Return the uptime of python, in second starting from 0

time.clock() >>> 6.182458438486231 Program

Random Library – Import random Randomise data

random.randrange(, )

random.randint(, ))

Generate integers between int_l and int_h Shuffling list

Randomise an integer between (Inclusive) integer_l and integer_h

random.shuffle()

random.uniform(