“格式化”字符串
“%s %e” % ("Value is", 16.0 ** 0.5) 显示一个字符串，后面跟着4.000000e+00。
"%7" % (11232/3) 显示计算结果，并用空格填充。
"%X" % 127 用16进制显示数字。
"%20s " % "Banana swirl" 把字符串填充到20位长，然后显示一个换行字符。 意味着换行。
"%s is $%4.2f" % (“Popsicle”, 1.754) 和字符串一样，显示一个2位十进制的浮点数。（16进制数会用来表示网页颜色之类的东西。）
“%s %f” % ("Value is",16.0 ** 0.5) 显示一个字符串，后面跟着4.000000。
“%07d” % (11232/3) 显示用0填充的值。 %后面的0意味着“用0填充”。
一个简单的pos程序：
def save_transaction(price,credit_card,description): file=open("transactions.txt", "a") file.write("%16s%07d%s " % (credit_card, price * 100, description)) file.close() items=["DONUT","LATTE","FILTER","MUFFIN"] prices=[1.50,2.0,1.80,1.20] running=True while running: option=1 for choice in items: print(str(option)+"."+choice) option=option+1 print(str(option)+".Quit") choice=int(input("Choose an option:")) if choice==option: running=False else: credit_card=input("Credit card number:") save_transaction(prices[choice-1],credit_card,items[choice-1])
运行结果：
Python 3.4.3 (v3.4.3:9b73f1c3e601, Feb 24 2015, 22:43:06) [MSC v.1600 32 bit (Intel)] on win32 Type "copyright", "credits" or "license()" for more information. >>> ================================ RESTART ================================ >>> 1.DONUT 2.LATTE 3.FILTER 4.MUFFIN 5.Quit Choose an option:2 Credit card number:63827462387648620000220 1.DONUT 2.LATTE 3.FILTER 4.MUFFIN 5.Quit Choose an option:3 Credit card number:63827462387648320000180 1.DONUT 2.LATTE 3.FILTER 4.MUFFIN 5.Quit Choose an option:5 >>>
进行模块化：
from transactions import *
items=["WORKOUT","WEIGHTS","BIKES"]
prices=[35.0,10.0,8.0]
running=True
while running:
option=1
for choice in items:
print(str(option)+"."+choice)
option=option+1
print(str(option)+".Quit")
choice=int(input("Choose an option:"))
if choice==option:
running=False
else:
credit_card=input("Credit card number:")
save_transaction(prices[choice-1],credit_card,items[choice-1])
from transactions import *
items=["DONUT","LATTE","FILTER","MUFFIN"]
prices=[1.50,2.0,1.80,1.20]
running=True
while running:
option=1
for choice in items:
print(str(option)+"."+choice)
option=option+1
print(str(option)+".Quit")
choice=int(input("Choose an option:"))
if choice==option:
running=False
else:
credit_card=input("Credit card number:")
save_transaction(prices[choice-1],credit_card,items[choice-1])
两个程序共用的程序（模块）
def save_transaction(price,credit_card,description):
file=open("transactions.txt", "a")
file.write("%07d%16s%16s
" % ( price * 100, credit_card, description))
file.close()
两个程序运行的结果：
Python 3.4.3 (v3.4.3:9b73f1c3e601, Feb 24 2015, 22:43:06) [MSC v.1600 32 bit (Intel)] on win32 Type "copyright", "credits" or "license()" for more information. >>> ================================ RESTART ================================ >>> 1.DONUT 2.LATTE 3.FILTER 4.MUFFIN 5.Quit Choose an option:1 Credit card number:6432425412474321 1.DONUT 2.LATTE 3.FILTER 4.MUFFIN 5.Quit Choose an option:5 >>> ================================ RESTART ================================ >>> 1.WORKOUT 2.WEIGHTS 3.BIKES 4.Quit Choose an option:1 Credit card number:7649463856424326 1.WORKOUT 2.WEIGHTS 3.BIKES 4.Quit Choose an option:4 >>>
价格下降了两次进行打折：
from transactions import *
import promotion
import starbuzz1
items=["DONUT","LATTE","FILTER","MUFFIN"]
prices=[1.50,2.0,1.80,1.20]
running=True
while running:
option=1
for choice in items:
print(str(option)+"."+choice)
option=option+1
print(str(option)+".Quit")
choice=int(input("Choose an option:"))
if choice==option:
running=False
else:
credit_card=input("Credit card number:")
price=promotion.discount(prices[choice-1])
if input("Starbuzz card")=="Y":
price=starbuzz1.discount(price)
save_transaction(price,credit_card,items[choice-1])
打9折：
def discount(price):
return 0.9*price
打95折：
def discount(price):
return 0.95*price
运行结果：
Python 3.4.3 (v3.4.3:9b73f1c3e601, Feb 24 2015, 22:43:06) [MSC v.1600 32 bit (Intel)] on win32 Type "copyright", "credits" or "license()" for more information. >>> ================================ RESTART ================================ >>> 1.DONUT 2.LATTE 3.FILTER 4.MUFFIN 5.Quit Choose an option:4 Credit card number:5413765853576543 Starbuzz cardN 1.DONUT 2.LATTE 3.FILTER 4.MUFFIN 5.Quit Choose an option:2 Credit card number:5413765853576543 Starbuzz cardY 1.DONUT 2.LATTE 3.FILTER 4.MUFFIN 5.Quit Choose an option: