《笨方法学 Python 》_ 习题 18 - 23

习题 18：命名、变量、代码和函数

# 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 里的 * 的功能是告诉 Python 把函数的所有参数都接收进来，然后放到名叫 args 的列表中去，一般不经常用到这个东西。

习题 19：函数和变量

函数里的变量和脚本里的变量之间是没有联系的，可以直接给函数传递数字，也可以给它变量，还可以给它数学表达式，甚至可以把数学表达式是和变量合起来用。

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)

习题 20：函数和文件

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() 函数用于移动文件读取指针到指定位置，file.seek(0) 回到了文件的开始。

readline() 函数会扫描文件的每一个字节，直到找到一个 \n 位置，然后它停止读取文件，并且返回此前的文件内容。file.readline() 文件 file 会记录每次调用 readline() 后的读取位置，这样它就可以在下次被调用时读取接下来的一行了。

习题 21：函数可以返回某些东西

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?")

习题 22：到现在你学到了哪些东西

回顾一下到现在为止已经学到的所有知识。

习题 23：阅读一些代码

使用目前学到的知识，看自己能不能读懂一些代码，看出它们的功能来。

《 笨方法学 Python 》_ 习题 18 - 23