1 方法一:用‘+’
示例：
test_str = 'hello' + ' ' + 'world'
print(test_str)
输出：hello world
- 优点：简洁方便
- 缺点：当有多个字符串相加拼接时，执行效率低下。因为字符串是不可变类型，相加以后会生成一个新的字符串，需要重新分配内存。当有多个字符串相加时，每加一次需要重新分配一次内存，多个字符相加需要相加多次，所以需要多次分配内存，从而导致效率低下。
- 适用场景：少量字符相加的场景
2 方法二：%s等格式化
示例：
tp1 = 'i am %s' % 'alex'
tp2='i am %s age %d' % ('alex', 18) //s对应字符串 d对应int
tp3='i am %(name)s age %(age)d' % {'name':'alex','age':18} // 通过key来取值
msg = 'iam %s,my hobby is %s' % ('lll',1) // s是万能的，对于int同样可用
print(msg) // iam lll,my hobby is 1
msg = 'iam %s,my hobby is %s' % ('lll',[1,2]) // s是万能的，对应list同样可用
print(msg) // iam lll,my hobby is [1, 2]
msg = 'iam %s,my hobby is %d' % ('lll',[1,2])
print(msg) //报错 TypeError: %d format: a number is required, not list
tp = 'percent %f' % 99.231465 //f 对应浮点数
print(tp) // percent 99.231465
tp = 'percent %.2f' % 99.231465 //2代表小数位数
print(tp) // percent 99.23
tp = 'percent %.2s' % 99.231465 //2代表字符串长度
print(tp) // percent 99
3 方法三：format格式化
tp = 'i am {}, age {}, {}'.format('lucy', 18, 'alex') //会自动一 一对应
print(tp) //i am lucy, age 18, alex
tp = 'i am {}, age {}, {}'.format('lucy', 18)
print(tp) //会报错，有三个{}，只有两个值
tp = 'i am {2}, age {1}, {0}'.format('lucy', 18, 'alex')
print(tp) //i am alex, age 18, lucy 按索引取值
tp = 'i am {1}, age {1}'.format('lucy', 18, 'alex')
print(tp) // i am 18, age 18 按索引取值
tp = 'i am {name}, age {age}, really {name}'.format(name='lucy', age=18)
print(tp) // i am lucy, age 18, really lucy 按key取值
tp = 'i am {name}, age {age}, really {name}'.format(**{'name':'lucy', 'age':18})
print(tp) //i am lucy, age 18, really lucy **后面是字典格式
tp = 'i am {}, age {}'.format(*['lucy', 18])
print(tp) // i am lucy, age 18 *后面是list格式
tp = 'i am {:s}, age {:d}'.format(*['lucy', 18])
print(tp) // i am lucy, age 18 s/d分别表示类型
tp = 'i am {:d}, age {:s}'.format(*['lucy', 18])
print(tp) //报错 ValueError: Unknown format code 'd' for object of type 'str'
tp = 'numbars:{:b},{:o},{:d},{:x},{:X},{:%}'.format(15,15,15,15,15,15)
print(tp) // numbars:1111,17,15,f,F,1500.000000%
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