【coursera 学习笔记】An Introduction to Interactive Programming in Python--week1

第一周 教学大纲

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Functions — Functions  函数

• Functions are reusable pieces of programs that take an input and produce an output.（定义）
• A function definition is a compound statement consisting of a header and a body.（组成）
• The header includes the keyword def, a sequence of parameters enclosed by parentheses, followed by a colon :.

• def  function_name():
             body
             return
  # computes the area of a triangle
  def triangle_area(base, height):     # header - ends in colon
      area = (1.0 / 2) * base * height # body - all of body is indented
      return area                      # body - return outputs value
  

  
  
  
• The body consists of a sequence of statements, all indented by 4 spaces.（缩进一般为4，注意同一逻辑层的缩进一致）
• Functions may return a value using the keyword return or have a side effect (e.g., print).
• To evaluate a function call, replace the function's parameters in the body of the function by their associated values in the call and execute the body of the function.
• Lecture examples - Functions
• More examples - Stucture of Functions, Uses of Functions, Scope of Variables, Examples of Functions

Indentation — Functions（缩进）

• Indentation consists of whitespace formed by blanks, tabs, and newlines.
• Leading white space indicates indentation level (4 spaces per level)and specifies logical grouping of statements in Python.
• Incorrect indentation can lead to errors.
• Lecture examples - Functions
• More examples - Function Errors

Remainders and modular arithmetic — More Operations

• Standard long division yields a quotient and a remainder. The integer division operator // computes the quotient. The operator % computes the remainder.
• For any integers a and b, a == b * (a // b) + (a % b).
• In Python, a % b always returns an answer that is between 0 and b (even if a and/or b is negative).
• Remainders and modular arithmetic are very useful in games for the purpose of "wrapping" the canvas, i.e; causing objects that pass off of one side of the canvas to reappear on the opposite side of the canvas.
• Lecture examples - More operations
• More examples - Modulus, Math Module,

Syntax:

a / b

a // b

Examples:

Code	Output
print 12 / 3	4
print 11 / 3	3
print 11 // 3	3
print 12.0 / 3.0	4.0
print 11.0 / 3.0	3.6666666666666665
print 11.0 // 3.0	3.0

/ 为标准除法：若a、b均为integer，则结果为对真值的向下取整（floor）。否则就是float

若a、b均为integer，则结果为对真值的向下取整（floor）。否则 在取整的前提下加上小数位.0

# problem - get the ones digit of a number
num = 49
tens = num // 10
ones = num % 10

Modules — More Operations

• Modules are libraries of Python code that implement useful operations not included in basic Python.
• Modules can be accessed via the import statement.
• CodeSkulptor implements parts of the standard Python modules math and random.
• Lecture examples - More operations
• More examples - Math Module, Numbers and Strings, Random Module, Module Errors

• # Python modules - extra functions implemented outside basic Python
  
  import simplegui	# access to drawing operations for interactive applications
  
  import math	 		# access to standard math functions, e.g; trig
  
  import random   	# functions to generate random numbers
  
  
  # look in Docs for useful functions
  
  print math.pi

  
  
  

Boolean Expressions — Logic and Comparisons

• The constants True and False of the type bool.
• These constants can be combined to form Boolean expressions via the logical operators and, or, and not.
• The and of two Boolean expressions is True if both of the expressions are True.
• The or of two Boolean expressions is True if at least one of the expressions is True.
• Lecture examples - None
• More examples - Booleans, Boolean Logic

Relational Operators — Logic and Comparisons

• The values of two arithmetic expressions can be compared using the operators ==, !=, <, >, <=, >=.
• These comparisons return either True or False .
• Lecture examples - None
• More examples - Comparison, Boolean Expressions

Conditional Statements — Conditionals

• Conditional statements are compound statements consisting one or more clauses headed by the keywords if, elif, and else.
• Each if or elif clause is followed by a Boolean expression and a colon :.
• If the Boolean expression for a clause is True, the body of the clause is executed.
• Lecture examples - Conditionals
• More examples - if-elif-else, Examples of Conditionals

• def num_solutions(discriminant):
      if discriminant > 0:
          return 2
      elif discriminant < 0:
          return 0
      else:
          return 1

  
  example：做界面

• # CodeSkulptor runs Python programs in your browser.
  # Click the upper left button to run this simple demo.
  
  # CodeSkulptor runs in Chrome 18+, Firefox 11+, and Safari 6+.
  # Some features may work in other browsers, but do not expect
  # full functionality.  It does NOT run in Internet Explorer.
  
  import simplegui
  
  message = "Welcome!"
  
  # Handler for mouse click
  def click():
      global message
      message = "Good job!"
  
  # Handler to draw on canvas
  def draw(canvas):
      canvas.draw_text(message, [50,112], 48, "Red")
  
  # Create a frame and assign callbacks to event handlers
  frame = simplegui.create_frame("Home", 300, 200)
  frame.add_button("Click me", click)
  frame.set_draw_handler(draw)
  
  # Start the frame animation
  frame.start()