第四章：字符串

fomat = "hello,%s,%s enough for ya!!"
values = ("world!","Hot")
# 字符串格式化时，如果对于的值是多个，值应该放在元祖中
print(fomat % values)

结果：
hello,world!,Hot enough for ya!!

# 简单转化
print("%s plus %s equal %s" % (1,2,3))
print("Price of eggs: $%d" % 42)
print("Price of eggs: $%x" % 42)

import math
print(math.pi)
print("pi:%f ..." % math.pi)

结果：
1 plus 2 equal 3
Price of eggs: $42
Price of eggs: $2a
3.141592653589793
pi:3.141593 ...

# 字段宽度与精度
from math import pi
# 10f表示宽度为10的浮点型
print("%10f" % pi)
# 10表示宽度，.后的2表示精度
print("%10.2f" % pi)
print("%.2f" % pi)
# 点（.)后跟精度值（可选）：如果转化的实数
# 精度值就表示出现在小数点后的位数
# 如果转化的是字符串，那么该数字就表示最大字段宽度
# 如果是“*”，那么精度会从元组中读取
print("%10.5s" % "python is great!")
print("%.5s" % "python is great!")
print("%*.*s" % (10,6,"python is great!"))
print("%.*s" % (3,"python is great!"))

结果：
  3.141593
      3.14
3.14
     pytho
pytho
    python
pyt

# 符号、对齐和用0填充
from math import pi
# "010"第1个0不是意味着八进制
# 表示宽度为10，并且用0填充空位
print("============0填充空位=============")
print("%10f" % pi)
print("%010f" % pi)
print("%10.2f" % pi)
print("%010.2f" % pi)
print("============‘-‘表示左对齐=============")
print("%10.2f" % pi)
print("%-10.2f" % pi)
print("============""表示正数前加上空格=============")
print("============"+"表示在转换之前加上正负号=============")
print(("% 5d" % 10) + "\n" + ("%5d" % -10))
print(("%+5d" % 10) + "\n" + ("%+5d" % -10))

结果：
============0填充空位=============
  3.141593
003.141593
      3.14
0000003.14
============‘-‘表示左对齐=============
      3.14
3.14      
============表示正数前加上空格=============
============表示在转换之前加上正负号=============
   10
  -10
  +10
  -10

# find方法，返回字符串最左端的索引
# 如果没找到则返回-1
title = "Monty python‘s Flying Circus!"
print(title.find("python"))
print(title.find("python",7))
print(title.find("python",6,20))

结果：
6
-1
6

# join方法
# 连接的序列元素必须是字符串
student_names = ["Alice","Bob","Bela"]
print("+".join(student_names))
#numbers = [1,2,3]
#print("+".join(numbers)) # 该语句会保存，原因：连接的序列元素必须是字符串
dirs = ("","home","bob")
dirs1 = ["","home","bob"]
print("/".join(dirs))
print("/".join(dirs1))
print("c:"+"\\".join(dirs))

结果：
Alice+Bob+Bela
/home/bob
/home/bob
c:\home\bob

sentence = "Hello world!"
print(sentence.split())
numbers = "1+2+3+4"
print(numbers.split())
print(numbers.split("+"))

结果：
[‘Hello‘, ‘world!‘]
[‘1+2+3+4‘]
[‘1‘, ‘2‘, ‘3‘, ‘4‘]

names = "Hello World!"
print(names.lower())
student_names = ["alice","bob","bela"]
student_name = "Bela"

if student_name.lower()in student_names:
    print(True)
else:
    print(False)

结果：
hello world!
True

# replace 方法
print("This is an apple.".replace("apple","orange"))
print("This is an apple apples.".replace("apple","orange"))
# replace 第3个参数，指定替换次数
print("This is an apple apples.".replace("apple","orange",1))

# strip方法
name = " Bela "
names = ["alice","leo","bela"]
namebak = name.lower()
if namebak.strip() in names:
    print(True)
else:
    print(False)

str = "*** python * for program language!***"
print(str.strip("*"))
print("*** python * for program language!***".strip("!"))
print("*** python * for program language!***".strip("*"))


结果：
True
 python * for program language!
*** python * for program language!***
 python * for program language!

str = "this is a string demo……wow!!"
intab = "aeiou"
outtab ="12345"
trantab = str.maketrans(intab,outtab)
print(trantab)
print(str.translate(trantab))

结果：
{97: 49, 101: 50, 105: 51, 111: 52, 117: 53}
th3s 3s 1 str3ng d2m4……w4w!!

# 字符串格式案例
# 使用给定的宽度，打印格式后的水果名称和价格
width = int(input("please input width:"))
price_width = 8
item_width = width - price_width
print("=" * width)
# header_format 表示表头，为字符串
# conFormat 表示内容，*.2f 价格为实数，精确到小数后2位
header_format = "%-*s%-*s"
conFormat = "%-*s%-*.2f"
print(header_format % (item_width,"Name",price_width,"Price"))
print("-" * width)
print(conFormat % (item_width,"Apple",price_width,5.89))
print(conFormat % (item_width,"Orange",price_width,4.123))
print(conFormat % (item_width,"Banana",price_width,3.1))


结果：

please input width:20
====================
Name        Price   
--------------------
Apple       5.89    
Orange      4.12    
Banana      3.10