python 常见字符串与函数的用法详解

s = \' abcd efg \'
print(s.strip())  #去除所有空格
print(s.lstrip())  #去除左边空格
print(s.rstrip())  #去除右边空格
print(s)
abcd efg
abcd efg 
 abcd efg
 abcd efg 

s = \'abc defg\'
print(s.upper())
print(s.upper().lower())
print(s.capitalize()) #首字母大写
ABC DEFG
abc defg
Abc defg

s_1 = \'abcdefg\'
s_2 = \'abdefgh\'
print(s_1.index(\'bcd\'))
try:
  print(s_1.index(\'bce\'))
except ValueError:
  print(\'ValueError: substring not found\')

print(s_1 == s_1)  # cmp函数被Python3移除了
print(s_1 > s_2)
print(s_2 > s_1)

1
ValueError: substring not found
True
False
True

s = \'\'
if not s:
  print(\'true\')
else:
  print(\'flase\') #空字符串和flase是等价的
true

s = \'abc,def,ghi\'
print(s.split(\',\'))
s = \'123\\n456\\n789\'
numbers = s.split(\'\\n\')  #按行分隔
numbers = s.splitlines() #按行分隔
print(numbers)
print(\'-\'.join(numbers)) 

[\'abc\', \'def\', \'ghi\']
[\'123\', \'456\', \'789\']
123-456-789

s = \'abcdefg\'
print(s.startswith(\'abc\'))  #判断是否以某个字符串为开头
print(s.endswith(\'efg\'))   #判断是否以某个字符串为结尾
print(\'abcd1234\'.isalnum())  #string中至少有一个字符，而且全是字母或者数字或者是字母和数字混合返回True，其他情况返回False
print(\'\\tabcd1234\'.isalnum()) 
print(\'abcd\'.isalpha())    #string中至少有一个字符，而且全为字母，返回True，其他情况返回False
print(\'12345\'.isdigit())   #输入字符串是否只由数字组成
print(\' \'.isspace())
print(\'acb125\'.islower())
print(\'A1B2C\'.isupper())
print(\'Hello world!\'.is ()) #检测字符串中所有的单词拼写首字母是否为大写，且其他字母为小写

True
True
True
False
True
True
True
True
True
False

def func(x, y = 500):
  print(x, y)
func(150)
func(100, 200)
func(y = 300, x = 100)
150 500
100 200
100 300

def func(name, *numbers): #加一个星号，就表示告诉python，在处理后面所有参数的时候，把这些参数放到一个数组里面
  print(name)
  print(numbers)
  print(type(numbers))
func(\'Tom\', 1, 2, 3, 4)
Tom
(1, 2, 3, 4)
<class \'tuple\'>    
#tuple - 元组，等价于只读数组，就是后面所有的参数都会作为一个数组

def func(name, **kvs): # **意思是把它装到 key/value 字典里，转化成字典了
  print(name)
  print(kvs)
  print(type(kvs))
func(\'Jack\', china = \'Beijing\', uk = \'London\')
Jack
{\'china\': \'Beijing\', \'uk\': \'London\'}
<class \'dict\'>

def func(a,b,c,*, china, uk): # *用于和普通参数做分割，*args一样效果
  print(china, uk)
func(1,2,3,china = \'Beijing\', uk = \'London\') # *后面传递的参数必须传入参数名
Beijing London

def func(a, b, c = 0, *args, **kvs):
  print(a, b, c, args, kvs)
func(1, 2)
func(1, 2, 3)
func(1, 2, 3, \'a\', \'b\')
func(1, 2, 3, \'a\', \'b\', china = \'Beijing\', uk = \'London\')
func(1, 2, 3, *(\'a\', \'b\'), **{\'china\':\'Beijing\', \'uk\':\'London\'}) #提高代码的可读性
1 2 0 () {}
1 2 3 () {}
1 2 3 (\'a\', \'b\') {}
1 2 3 (\'a\', \'b\') {\'china\': \'Beijing\', \'uk\': \'London\'}
1 2 3 (\'a\', \'b\') {\'china\': \'Beijing\', \'uk\': \'London\'}
def my_print(*args):
  print(*args) #传变量时，在变量前加上*号，代表把这个数组作为可变参数处理
  my_print(\'x = \',100, \'y = \',200)
x = 100 y = 200

def sum(x,y,p = None):
  s = x + y 
  if p:
    p(s)
  return 


sum(100,200)
sum(100,200,print)

300
def cmp(x,y,cp = None):
  if not cp:
    if x > y:
      return 1
    elif x < y:
      return -1
    else:
      return 0
  else:
    return cp(x,y)

def my_cp(x ,y):
  if x < y:
    return 1
  elif x == y:
    return 0
  else:
    return -1

print(cmp(100,200))
print(cmp(100,200,my_cp))

-1
1

def my_sum(i):
  if i < 0:
    raise ValueError
  elif i <=1:
    return i
  else:
    return i + my_sum(i - 1) # my_sum(i - 1)是它更小范围内的解，利用这个子问题的解得出当前的解

print(my_sum(1))
print(my_sum(2))
print(my_sum(3))
print(my_sum(10))
print(my_sum(100))
1
3
6
55
5050
# 递归的经典例子！
# 斐波那契数列 f(n) = f(n - 1) + f(n -2)
def fib(n):
  if n < 1:
    raise ValueError
  elif (n == 1) or (n == 2):
    return 1
  else:
    return fib(n - 1) + fib(n - 2)
print(fib(1))
print(fib(2))
print(fib(3))
print(fib(4))
print(fib(5))
print(fib(6))
1
1
2
3
5
8