習題 18：命名、變數、程式碼和函式

# this one is like your scripts with argv
def print_two(*args):
    arg1, arg2 = args
    print("arg1: %r, arg2: %r" % (arg1, arg2))
    
# ok, that *argv is actually pointless, we can just do this
def print_two_again(arg1, arg2):
    print("arg1: %r, arg2: %r" % (arg1, arg2))
    
# this just takes one argument
def print_one(arg1):
    print("arg1: %r" % arg1)
    
#this one takes no arguments
def print_none():
    print("I got nothing.")
    
    
print_two("Zed", "Shaw")
print_two_again("Zed", "Shaw")
print_one("First!")
print_none()
 

*args 裡的 * 的功能是告訴 Python 把函式的所有引數都接收進來，然後放到名叫 args 的列表中去，一般不經常用到這個東西。

習題 19：函式和變數

函式裡的變數和腳本里的變數之間是沒有聯絡的，可以直接給函式傳遞數字，也可以給它變數，還可以給它數學表示式，甚至可以把數學表示式是和變數合起來用。

def cheese_and_crackers(cheese_count, boxes_of_crackers):
    print("You hace %d cheese!" % cheese_count)
    print("You hace %d boxes pf crackers!" % boxes_of_crackers)
    print("Man that's enough for a party!")
    print("Get a blanket.\n")
        
print("We can just give the function numbers directly:")
cheese_and_crackers(20, 30)

print("OR, we can use variables from our script:")
amount_of_cheese = 10
amount_of_crackers = 50

cheese_and_crackers(amount_of_cheese, amount_of_crackers)

print("We can even do math inside too:")
cheese_and_crackers(10 + 20, 5 + 6)

print("And we can combine the two, variables and math:")
cheese_and_crackers(amount_of_cheese + 100, amount_of_crackers + 1000)
 

習題 20：函式和檔案

from sys import argv

script, input_file = argv

def print_all(f):
    print(f.read())
    
def rewind(f):
    f.seek(0)
    
def print_a_line(line_count, f):
    print(line_count, f.readline())

current_file = open(input_file)

print("First let's print the whole file:\n")

print_all(current_file)

print("Now let's rewind, kind of like a tape.")

rewind(current_file)

print("Let's print three lines:")

current_line = 1
print_a_line(current_line, current_file)

current_line = current_line + 1
print_a_line(current_line, current_file)

current_line = current_line + 1
print_a_line(current_line, current_file)
 

seek() 函式用於移動檔案讀取指標到指定位置，file.seek(0) 回到了檔案的開始。

readline() 函式會掃描檔案的每一個位元組，直到找到一個 \n 位置，然後它停止讀取檔案，並且返回此前的檔案內容。file.readline()   檔案 file 會記錄每次呼叫 readline() 後的讀取位置，這樣它就可以在下次被呼叫時讀取接下來的一行了。

習題 21：函式可以返回某些東西

def add(a, b):
    print("Adding %d + %d" % (a, b))
    return a + b

def subtract(a, b):
    print("Subtracting %d - %d" % (a, b))
    return a - b
    
def multiply(a, b):
    print("Multiplying %d * %d" % (a, b))
    return a * b
    
def divide(a, b):
    print("Dividing %d / %d" % (a, b))
    return a / b
    
print("Let's do some math with just function!")

age = add(20, 5)
height = subtract(180, 2)
weight = multiply(90, 2)
iq = divide(200, 2)

print("Age: %d, Height: %d, Weight: %d, IQ: %d" % (age, height, weight, iq))

# A puzzle for the extra credit, type it in anyway.
print("Here is a puzzle.")

what = add(age, subtract(height, multiply(weight, divide(iq, 2))))

print("That becomes:", what, "Can you do it by hand?")

習題 22：到現在你學到了哪些東西

回顧一下到現在為止已經學到的所有知識。

習題 23：閱讀一些程式碼

使用目前學到的知識，看自己能不能讀懂一些程式碼，看出它們的功能來。