python3.6.4的學習

時間 2019-11-10

原文原文鏈接

[root@mantisbt01 python]# ./13.py
Please input your name:hadoop
Please input your height(m):1.80
Please input your height(kg):75.3
hadoop , Your bmi value is: 23.24 !
Your body type is 正常
[root@mantisbt01 python]# python
Python 3.6.4 (default, Mar 19 2018, 10:30:22)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-16)] on linux
Type "help", "copyright", "credits" or "license" for more information.python

abs(12)
12
abs(-12)
12
abs(0)
0
abs(-12.3)
12.3
abs(12.3)
12.3
abs(1,2)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: abs() takes exactly one argument (2 given)
abs(f)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'f' is not defined
max(1,2)
2
max(1,2,23,4)
23
max(1,2,23,4,-9,0)
23
int(321)
321
int(12.32)
12
float(12.32)
12.32
float(12)
12.0
float('12.32')
12.32
str(100)
'100'
str(13)
'13'
str(as)
File "<stdin>", line 1
str(as)
^
SyntaxError: invalid syntax
str('as')
'as'
str('a')
'a'
str(a)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'a' is not defined
bool(1)
True
bool(-1)
True
bool(0)
False
bool(a)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'a' is not defined
bool('a')
True
a=abs
a(-2)
2
n1=255
n2=1000
hex(n1)
'0xff'
hex(n2)
'0x3e8'linux

def my_abs(x):
... if x >=0:
... return x
... else:
... return -x
...
my_abs(-9)
9
my_abs(-8)
8
my_abs(8)
8
my_abs(0)
0
my_abs(a)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 2, in my_abs
TypeError: '>=' not supported between instances of 'builtin_function_or_method' and 'int'
my_abs('a')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 2, in my_abs
TypeError: '>=' not supported between instances of 'str' and 'int'git

[root@mantisbt01 python]# pwd
/root/python
[root@mantisbt01 python]# cat 14.py
def my_abs(x):
if x >=0:
return x
else:
return -x
[root@mantisbt01 python]# python
Python 3.6.4 (default, Mar 19 2018, 10:30:22)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-16)] on linux
Type "help", "copyright", "credits" or "license" for more information.算法

from 14 import my_abs
File "<stdin>", line 1
from 14 import my_abs
^
SyntaxError: invalid syntaxexpress

KeyboardInterrupt編程

[root@mantisbt01 python]# mv 14.py abstest.py
[root@mantisbt01 python]# python
Python 3.6.4 (default, Mar 19 2018, 10:30:22)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-16)] on linux
Type "help", "copyright", "credits" or "license" for more information.
from abstest import my_abs
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/root/python/abstest.py", line 3
return x
^
TabError: inconsistent use of tabs and spaces in indentationapi

[root@mantisbt01 python]# vi abstest.py
[root@mantisbt01 python]# python
Python 3.6.4 (default, Mar 19 2018, 10:30:22)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-16)] on linux
Type "help", "copyright", "credits" or "license" for more information.
from abstest import my_abs
my_abs(-18)
18
my_abs(19)
19
my_abs(0)
0
my_abs('a')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/root/python/abstest.py", line 2, in my_abs
if x >=0:
TypeError: '>=' not supported between instances of 'str' and 'int'
my_abs(a)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'a' is not defined數組

def nop():
... pass
...app

if age >=18:
... pass
...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'age' is not defined
age=10
if age >=18:
... age
...編程語言

my_abs(2)
2
my_abs(1,2)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: my_abs() takes 1 positional argument but 2 were given
my_abs('A')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/root/python/abstest.py", line 2, in my_abs
if x >=0:
TypeError: '>=' not supported between instances of 'str' and 'int'
abs('A')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: bad operand type for abs(): 'str'

[root@mantisbt01 python]# cp -p abstest.py abstest2.py
[root@mantisbt01 python]#
[root@mantisbt01 python]# vi abstest2.py
[root@mantisbt01 python]# cat abstest2.py
def my_abs(x):
if not isinstance(x,(int,float)):
raise TypeError('bad operand type')
if x >=0:
return x
else:
return -x
[root@mantisbt01 python]#

[root@mantisbt01 python]# cp -p abstest.py abstest2.py
[root@mantisbt01 python]#
[root@mantisbt01 python]# vi abstest2.py
[root@mantisbt01 python]# cat abstest2.py
def my_abs(x):
if not isinstance(x,(int,float)):
raise TypeError('bad operand type')
if x >=0:
return x
else:
return -x
[root@mantisbt01 python]# python
Python 3.6.4 (default, Mar 19 2018, 10:30:22)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-16)] on linux
Type "help", "copyright", "credits" or "license" for more information.

from abstest2 import my_abs
my_abs(-9)
9
my_abs(9)
9
my_abs(0)
0
my_abs('A')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/root/python/abstest2.py", line 3, in my_abs
raise TypeError('bad operand type')
TypeError: bad operand type

import math
def move(x,y,step,angle=0):
... nx = x + step math.cos(angle)
... ny = y + step math.sin(angle)
... return nx,ny
...
x,y=move(100,100,60,math.pi / 6)
print(x,y)
151.96152422706632 130.0
r = move(100,100,60,math.pi / 6)
print(r)
(151.96152422706632, 130.0)

r
(151.96152422706632, 130.0)

[root@mantisbt01 python]# cat 14.py
#!/usr/bin/python

#-- coding: utf-8 --

import math
def quadratic(a,b,c):
if not ( isinstance(a,(int,float)) and isinstance(b,(int,float)) and isinstance(c,(int,float)) ):
raise TypeError('bad operand type')
delta=(b*2)-(4bc)
if delta < 0:
print('delta小於零,方程無解')
else:
x1=(-b+math.sqrt(delta))/(2a)
x2=(-b-math.sqrt(delta))/(2*a)
print('x1=%.2f x2=%.2f'%(x1,x2))
return x1,x2

print('quadratic(2,3,1)=',quadratic(2,3,1))
print('quadratic(1,3,-4)=',quadratic(1,3,-4))
[root@mantisbt01 python]# ./14.py
delta小於零,方程無解
quadratic(2,3,1)= None
x1=2.27 x2=-5.27
quadratic(1,3,-4)= (2.274917217635375, -5.274917217635375)
[root@mantisbt01 python]#

def power(x):
... return x*x
...
power(4)
16
power(2)
4
power(3)
9
power(11)
121

def power(x,n)
File "<stdin>", line 1
def power(x,n)
^
SyntaxError: invalid syntax
def power(x,n):
... s=1
... while n > 0:
... n=n-1
... s=s*x
... return s
...
power(2,3)
8
power(3,3)
27
power(3,4)
81

power(5)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: power() missing 1 required positional argument: 'n'
def power(x,n=2):
... s=1
... while n > 0:
... n=n-1
... s=sx
... return
...
power(5)
def power(x,n=2):
... s=1
... while n > 0:
... n=n-1
... s=sx
... return s
...
power(5)
25
power(3)
9
power(3,4)
81

def enroll(name,gender):
... print('name:',name)
... print('gender:',gender)
...
enroll('Sarah','F')
name: Sarah
gender: F
def enroll(name,gender,age=6,city='Beijing'):
... print('name:',name)
... print('gender',gender)
... print('age:',age)
... print('city:',city)
...

enroll('Sarah','F')
name: Sarah
gender F
age: 6
city: Beijing
enroll('Bob','M',8)
name: Bob
gender M
age: 8
city: Beijing
enroll('Adam','M',city='shanghai')
name: Adam
gender M
age: 6
city: shanghai

def add_end(L=[]):
... L.append('END')
... return L
...
add_end([1,2,3])
[1, 2, 3, 'END']
add_end(['x','y','z'])
['x', 'y', 'z', 'END']
add_end([1,2,3])
[1, 2, 3, 'END']
add_end()
['END']
add_end()
['END', 'END']
add_end()
['END', 'END', 'END']
add_end()
['END', 'END', 'END', 'END']
def add_end(L=[]):
... if L is None:
... L=[]
... L.append('END')
... return L
...
add_end()
['END']
add_end()
['END', 'END']
add_end()
['END', 'END', 'END']
def add_end(L=None):
... if L is None:
... L=[]
... L.append('END')
... return L
...
add_end()
['END']
add_end()
['END']
add_end()
['END']

def calc(number):
... sum=0
... for n in number:
... sum=sum+n*n
... return sum
...
calc([1,2,3])
14
calc([1,2,3,4])
30
calc(1,2,3)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: calc() takes 1 positional argument but 3 were given

def calc(number):
... sum=0
... for n in number:
... sum=sum+nn
... return sum
...
calc(1,2,3)
14
calc([1,2,3])
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 4, in calc
TypeError: can't multiply sequence by non-int of type 'list'
calc(1,2,3,4)
30

calc(1,2)
5
calc()
0
nums = [1,2,3]
calc(nums[0],nums[1],nums[2])
14
calc(*nums)
14

關鍵字參數

def person(name,age,**kw):
... print('name:',name,'age:',age,'other:',kw)
...

person('Michael',30)
name: Michael age: 30 other: {}
person('Bob',35,city='Beijing')
name: Bob age: 35 other: {'city': 'Beijing'}
person('Adam',45,gender='M',job='Engineer')
name: Adam age: 45 other: {'gender': 'M', 'job': 'Engineer'}

extra={'city':'Beijing','job':'Engineer'}
person('Jack',24,city=extra['city'],job=extra['job'])
name: Jack age: 24 other: {'city': 'Beijing', 'job': 'Engineer'}

person('Jack',24,**extra)
name: Jack age: 24 other: {'city': 'Beijing', 'job': 'Engineer'}

extra表示把extra這個dict的全部key-value用關鍵字參數傳入到函數的kw參數，kw將得到一個dict，注意kw得到的dict是extra的一份拷貝，對kw的改動不會影響到函數外的extra.

命名關鍵字參數

def person(name,age,**kw):
... if 'city' in kw:
... pass
... if 'job' in kw:
... pass
... print('name',name,'age',age,'other:',kw)
...
person('Jack',24,city='Beijing',addr='Chaoyang',zipcode=123456)
name Jack age 24 other: {'city': 'Beijing', 'addr': 'Chaoyang', 'zipcode': 123456}

def person(name,age,*,city,job):
... print(name,age,city,job)
...
person('Jack',24,city='Beijing',job='Engineer')
Jack 24 Beijing Engineer

若是函數定義中已經有了一個可變參數，後面跟着的命名關鍵字參數就再也不須要一個特殊分隔符*了：

def person(name,age,*args,city,job):
... print(name,age,args,city,job)
...
person('Jack',24,'Beijing','Engineer')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: person() missing 2 required keyword-only arguments: 'city' and 'job'
person('Jack',24,city='Beijing','Engineer')
File "<stdin>", line 1
SyntaxError: positional argument follows keyword argument
person('Jack',24,city='Beijing',job='Engineer')
Jack 24 () Beijing Engineer

命名關鍵字參數能夠有缺省值，從而簡化調用：

def person(name,age,*,city='Beijing',job):
... print(name,age,city,job)
...
因爲命名關鍵字參數city具備默認值，調用時，可不傳入city參數：
person('Jack',24,job='Engineer')
Jack 24 Beijing Engineer

參數組合

def f1(a,b,c=0,*args,**kw):
... print('a=',a,'b=',b,'c=',c,'args=',args,'kw=',kw)
...

def f2(a,b,c=0,*,d,**kw):
... print('a=',a,'b=',b,'c=',c,'d=',d,'kw=',kw)
...

f1(1,2)
a= 1 b= 2 c= 0 args= () kw= {}
f1(1,2,c=3)
a= 1 b= 2 c= 3 args= () kw= {}
f1(1,2,'a','b')
a= 1 b= 2 c= a args= ('b',) kw= {}
f1(1,2,3,'a','b')
a= 1 b= 2 c= 3 args= ('a', 'b') kw= {}
f1(1,2,3,'a','b','c')
a= 1 b= 2 c= 3 args= ('a', 'b', 'c') kw= {}
f1(1,2,3,'a','b','c',x=98)
a= 1 b= 2 c= 3 args= ('a', 'b', 'c') kw= {'x': 98}

f2(1,2,d=23,ext=None)
a= 1 b= 2 c= 0 d= 23 kw= {'ext': None}

經過一個tuple和dict，也能夠調用上述函數：

args=(1,2,3,4)

kw={'d':99,'x':'#'}

f1(*args,**kw)
a= 1 b= 2 c= 3 args= (4,) kw= {'d': 99, 'x': '#'}

f2(*args,**kw)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: f2() takes from 2 to 3 positional arguments but 4 positional arguments (and 1 keyword-only argument) were given

args=(1,2,3)

kw={'d':88,'x':'#'}

f2(*args,**kw)
a= 1 b= 2 c= 3 d= 88 kw= {'x': '#'}

[root@mantisbt01 python]# cat ./15.py
#!/usr/bin/python

#-- coding:utf-8 --

def product(numbers):
product=1
if numbers==():
raise TypeError
else:
for n in numbers:
product=product n

print('product =',product)

return product

#test
print('product(5) =',product(5))
print('product(5,6) =',product(5,6))
print('product(5,6,7) =',product(5,6,7))
print('product(5,6,7,9) =',product(5,6,7,9))

if product(5) != 5:
print('test failed!')
elif product(5,6) != 30:
print('test failed!')
elif product(5,6,7) != 210:
print('test failed!')
elif product(5,6,7,9) != 1890:
print('test failed!')
else:
try:
product()
print('test failed!')
except TypeError:
print('test successful')
[root@mantisbt01 python]# ./15.py
product(5) = 5
product(5,6) = 30
product(5,6,7) = 210
product(5,6,7,9) = 1890
test successful
[root@mantisbt01 python]#

遞歸函數

def fact(n):
... if n==1:
... return 1
... return n*fact(n-1)
...
fact(1)
1
fact(5)
120
fact(100)
93326215443944152681699238856266700490715968264381621468592963895217599993229915608941463976156518286253697920827223758251185210916864000000000000000000000000
fact(1000)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 4, in fact
File "<stdin>", line 4, in fact
File "<stdin>", line 4, in fact
[Previous line repeated 994 more times]
File "<stdin>", line 2, in fact
RecursionError: maximum recursion depth exceeded in comparison

[root@mantisbt01 python]# python
Python 3.6.4 (default, Mar 19 2018, 10:30:22)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-16)] on linux
Type "help", "copyright", "credits" or "license" for more information.

def fact(n):
... return fact_iter(n,1)
...
def fact_iter(num,product):
... if num==1:
... return product
... return fact_iter(num-1,num*product)
...
fact_iter(5,1)
120
fact_iter(10,1)
3628800
fact_iter(1,1)
1
fact_iter(20,1)
2432902008176640000
fact_iter(1000,1)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 4, in fact_iter
File "<stdin>", line 4, in fact_iter
File "<stdin>", line 4, in fact_iter
[Previous line repeated 994 more times]
File "<stdin>", line 2, in fact_iter
RecursionError: maximum recursion depth exceeded in comparison

fact(10)
3628800
def fact(n):
... s=1
... for i in range(1,n+1):
... s=si
... return s
...
fact(10)
3628800
fact(5)
120
from functools import reduce
def Fact(n):
... return reduce((lambda x,y:xy),list(range(1,n+1)))
...
Fact(5)
120
Fact(10)
3628800

漢諾塔的移動能夠用遞歸函數很是簡單地實現。

請編寫move(n, a, b, c)函數，它接收參數n，表示3個柱子A、B、C中第1個柱子A的盤子數量，而後打印出把全部盤子從A藉助B移動到C的方法，例如：
[root@mantisbt01 python]# cat ./17.py
#!/usr/bin/python

#-- coding:utf-8 --

def move(n,a,b,c):
if n==1:
step=1
print(a,'-->',c)
return step
else:
s1=move(n-1,a,c,b)
s2=move(1,a,b,c)
s3=move(n-1,b,a,c)
step=s1+s2+s3
return step

s=move(3,'A','B','C')
print('need %d steps'%s)
[root@mantisbt01 python]# ./17.py
A --> C
A --> B
C --> B
A --> C
B --> A
B --> C
A --> C
need 7 steps
[root@mantisbt01 python]#

高級特性
好比構造一個1, 3, 5, 7, ..., 99的列表，能夠經過循環實現：

L = []
n = 1
while n <= 99:
L.append(n)
n = n + 2
取list的前一半的元素，也能夠經過循環實現。

可是在Python中，代碼不是越多越好，而是越少越好。代碼不是越複雜越好，而是越簡單越好。

基於這一思想，咱們來介紹Python中很是有用的高級特性，1行代碼能實現的功能，決不寫5行代碼。請始終牢記，代碼越少，開發效率越高。
法1：

L=[]
n=1
while n<=99:
... L.append(n)
... n=n+2
...
L
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 87, 89, 91, 93, 95, 97, 99]

法2：

print(list(range(1,100,2)))
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 87, 89, 91, 93, 95, 97, 99]

法3：

print([i for i in range(1,100,2)])
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 87, 89, 91, 93, 95, 97, 99]

1.切片
1.1 list

L=['Michael','Sarah','Tracy','Bob','Jack']
[L[0],L[1],L[2]]
['Michael', 'Sarah', 'Tracy']
[L[-1],L[-2],L[-3]]
['Jack', 'Bob', 'Tracy']
r=[]
n=3
for i in range(n):
... r.append(L[i])
...
r
['Michael', 'Sarah', 'Tracy']
L[0:3]
['Michael', 'Sarah', 'Tracy']
L[0:4]
['Michael', 'Sarah', 'Tracy', 'Bob']
L[1:3]
['Sarah', 'Tracy']
L[:3]
['Michael', 'Sarah', 'Tracy']
L[-2:]
['Bob', 'Jack']
L[-2:-1]
['Bob']
L[-1]
'Jack'
L=list(range(100))
L
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99]
L[:10]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
L[-10:]
[90, 91, 92, 93, 94, 95, 96, 97, 98, 99]
L[10:20]
[10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
L[2:10:2]
[2, 4, 6, 8]
L[2:10:3]
[2, 5, 8]
L[::5]
[0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95]
L[:]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99]

1.2 tuple

(0,1,2,3,4,5)[:3]
(0, 1, 2)
'ABCDEFG'[:3]
'ABC'
'ABCDEFG'[::2]
'ACEG'

利用切片操做，實現一個trim()函數，去除字符串首尾的空格，注意不要調用str的strip()方法：
[root@mantisbt01 python]# cat 18.py
#!/usr/bin/python

#-- coding:utf-8 --

#def trim(s):

if len(s) == 0:

return s

elif s[0] == '':

return (trim(s[1:]))

elif s[-1] == ' ':

return (trim(s[:-1]))

return s

def trim(s):
if s[:1] != ' ' and s[-1:] != ' ':
return s
elif s[:1] == ' ':
return trim(s[1:])
else:
return trim(s[:-1])

if trim('hello ') != 'hello':
print('測試失敗!')
elif trim(' hello') != 'hello':
print('測試失敗!')
elif trim(' hello ') != 'hello':
print('測試失敗!')
elif trim(' hello world ') != 'hello world':
print('測試失敗!')
elif trim('') != '':
print('測試失敗!')
elif trim(' ') != '':
print('測試失敗!')
else:
print('測試成功!')
[root@mantisbt01 python]# ./18.py
測試成功!

2.迭代

d={'a':1,'b':2,'c':3}
for key in d:
... print(key)
...
a
b
c
for ch in 'ABC':
... print(ch)
...
A
B
C

from collections import Iterable
isinstance('abc',Iterable)
True
isinstance([1,2,3],Iterable)
True
isinstance(123,Iterable)
False

for i,value in enumerate(['A','B','C']):
... print(i,value)
...
0 A
1 B
2 C
for x,y in [(1,1),(2,4),(3,9)]:
... print(x,y)
...
1 1
2 4
3 9

請使用迭代查找一個list中最小和最大值，並返回一個tuple：
使用冒泡排序法
[root@mantisbt01 python]# cat 19.py
#!/usr/bin/python

#-- coding:utf-8 --

def findMinandMax(L):
if (L==[]):
return (None,None)
else:
num=len(L)
for i in range(num):
for j in range(i):
if L[i]<L[j]:
L[i],L[j]=L[j],L[i]
return (L[0],L[-1])

if findMinandMax([]) != (None,None):
print('測試失敗!')
elif findMinandMax([7]) != (7,7):
print('測試失敗!')
elif findMinandMax([7,1]) != (1,7):
print('測試失敗!')
elif findMinandMax([7,1,3,9,5]) != (1,9):
print('測試失敗!')
else:
print('測試成功')
[root@mantisbt01 python]#
[root@mantisbt01 python]# ./19.py
測試成功

3.列表生成式

list(range(1,11))
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
L=[]
for x in range(1,11):
... L.append(xx)
...
L
[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
[xx for x in range(1,11)]
[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

[x*x for x in range(1,11) if x%2 == 0]
[4, 16, 36, 64, 100]

[m+n for m in 'ABC' for n in 'XYZ']
['AX', 'AY', 'AZ', 'BX', 'BY', 'BZ', 'CX', 'CY', 'CZ']

import os
[d for d in os.listdir('.')]
['18.py', '19.py', '1.py', '2.py', '3.py', '4.py', '5.py', '6.py', '7.py', '8.py', '9.py', '10.py', '11.py', '12.py', '13.py', 'abstest.py', 'pycache', 'abstest2.py', '14.py', '15.py', '16.py', '17.py']

[d for d in os.listdir('/')]
['boot', 'dev', 'proc', 'run', 'sys', 'etc', 'root', 'var', 'tmp', 'usr', 'bin', 'sbin', 'lib', 'lib64', 'home', 'media', 'mnt', 'opt', 'srv', '.autorelabel']

[d for d in os.listdir('/home')]
['test2', 'test3', 'test4', 'test1']

d={'x':'A','y':'B','z':'C'}
for k,v in d.items():
... print(k,'=',v)
...
x = A
y = B
z = C

d={'x':'A','y':'B','z':'C'}
[k+'='+v for k,v in d.items()]
['x=A', 'y=B', 'z=C']
L=['Hello','World','IBM','Apple']
[s.lower() for s in L]
['hello', 'world', 'ibm', 'apple']

L=['Hello','World',18,'IBM','Apple']
[s.lower() for s in L]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 1, in <listcomp>
AttributeError: 'int' object has no attribute 'lower'

[root@mantisbt01 python]# cat 20.py
#!/usr/bin/python

#-- coding:utf-8 --

L1=['Hello','World',18,'IBM',None]
L2=[s.lower() for s in L1 if isinstance(s,str)]

print(L2)
if L2 == ['hello','world','ibm']:
print('測試經過!')
else:
print('測試失敗')
[root@mantisbt01 python]# ./20.py
['hello', 'world', 'ibm']
測試經過!
[root@mantisbt01 python]#

4.生成器

L=[x*x for x in range(10)]
L
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

g=(x*x for x in range(10))
g
<generator object <genexpr> at 0x7f8ab91c8570>
next(g)
0
next(g)
1
next(g)
4
next(g)
9
next(g)
16
next(g)
25
next(g)
36
next(g)
49
next(g)
64
next(g)
81
next(g)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
StopIteration

g=(x*x for x in range(10))
for n in g:
... print(n)
...
0
1
4
9
16
25
36
49
64
81
def fib(max):
... n,a,b=0,0,1
... while n < max:
... print(b)
... a,b=b,a+b
... n=n+1
... return 'done'
...
fib(6)
1
1
2
3
5
8
'done'

def fib(max):
... n,a,b=0,0,1
... while n < max:
... yield b
... a,b=b,a+b
... n=n+1
... return 'done'
...
f=fib(6)
f
<generator object fib at 0x7f8ab91c8620>

def odd():
... print('step 1')
... yield 1
... print('step 2')
... yield(3)
... print('step 3')
... yield(5)
...
o=odd()
next(o)
step 1
1
next(o)
step 2
3
next(o)
step 3
5
next(o)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
StopIteration
for n in fib(6):
... print(n)
...
1
1
2
3
5
8
g=fib(6)
while True:
... try:
... x=next(g)
... print('g:',x)
... except StopIteration as e:
... print('Generator return value:',e.value)
... break
...
g: 1
g: 1
g: 2
g: 3
g: 5
g: 8
Generator return value: done

練習

[root@mantisbt01 python]# cat ./21.py
#!/usr/bin/python

#-- coding:utf-8 --

def triangles():
L=[1]
while True:
yield L
L = [x+y for x,y in zip([0]+L,L+[0])]

n = 0
results = []
for t in triangles():
print(t)
results.append(t)
n = n + 1
if n == 10:
break
if results == [
[1],
[1, 1],
[1, 2, 1],
[1, 3, 3, 1],
[1, 4, 6, 4, 1],
[1, 5, 10, 10, 5, 1],
[1, 6, 15, 20, 15, 6, 1],
[1, 7, 21, 35, 35, 21, 7, 1],
[1, 8, 28, 56, 70, 56, 28, 8, 1],
[1, 9, 36, 84, 126, 126, 84, 36, 9, 1]
]:
print('測試經過!')
else:
print('測試失敗!')
[root@mantisbt01 python]# ./21.py
[1]
[1, 1]
[1, 2, 1]
[1, 3, 3, 1]
[1, 4, 6, 4, 1]
[1, 5, 10, 10, 5, 1]
[1, 6, 15, 20, 15, 6, 1]
[1, 7, 21, 35, 35, 21, 7, 1]
[1, 8, 28, 56, 70, 56, 28, 8, 1]
[1, 9, 36, 84, 126, 126, 84, 36, 9, 1]
測試經過!
[root@mantisbt01 python]# cat ./22.py
#!/usr/bin/python

#-- coding:utf-8 --

def triangles():
L=[1]
while True:
yield L
L = [x+y for x,y in zip([0]+L,L+[0])]

n = 0
results = []
for t in triangles():
print(t)
results.append(t)
n = n + 1
if n == 15:
break
[root@mantisbt01 python]# ./22.py
[1]
[1, 1]
[1, 2, 1]
[1, 3, 3, 1]
[1, 4, 6, 4, 1]
[1, 5, 10, 10, 5, 1]
[1, 6, 15, 20, 15, 6, 1]
[1, 7, 21, 35, 35, 21, 7, 1]
[1, 8, 28, 56, 70, 56, 28, 8, 1]
[1, 9, 36, 84, 126, 126, 84, 36, 9, 1]
[1, 10, 45, 120, 210, 252, 210, 120, 45, 10, 1]
[1, 11, 55, 165, 330, 462, 462, 330, 165, 55, 11, 1]
[1, 12, 66, 220, 495, 792, 924, 792, 495, 220, 66, 12, 1]
[1, 13, 78, 286, 715, 1287, 1716, 1716, 1287, 715, 286, 78, 13, 1]
[1, 14, 91, 364, 1001, 2002, 3003, 3432, 3003, 2002, 1001, 364, 91, 14, 1]
[root@mantisbt01 python]#

from collections import Iterable
isinstance([],Iterable)
True
isinstance({},Iteranle)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'Iteranle' is not defined
from collections import Iterable
isinstance([],Iterable)
True
isinstance({},Iterable)
True
isinstance('abc',Iterable)
True
isinstance(x for x in range(10),Iterable)
File "<stdin>", line 1
SyntaxError: Generator expression must be parenthesized if no t sole argument
isinstance((x for x in range(10)),Iterable)
True
isinstance(100,Iterable)
False

from collections import Iterator
isinstance((x for x in range(10)),Iterator)
True
isinstance([],Iterator)
False
isinstance({},Iterator)
False
isinstance('ABC',Iterator)
False
isinstance(100,Iterator)
False
isinstance(iter([]),Iterator)
True
isinstance(iter('abc'),Iterator)
True

for x in [1,2,3,4,5]:
... pass
...
for x in [1,2,3,4,5]:
... print(x)
...
1
2
3
4
5

it=iter([1,2,3,4,5])
while True:
... try:
... x=next(it)
... print(x)
... except StopIteration:
... break
...
1
2
3
4
5

凡是可做用於for循環的對象都是Iterable類型；

凡是可做用於next()函數的對象都是Iterator類型，它們表示一個惰性計算的序列；

集合數據類型如list、dict、str等是Iterable但不是Iterator，不過能夠經過iter()函數得到一個Iterator對象。

函數式編程

函數式編程就是一種抽象程度很高的編程範式，純粹的函數式編程語言編寫的函數沒有變量，所以，任意一個函數，只要輸入是肯定的，輸出就是肯定的，這種純函數咱們稱之爲沒有反作用。而容許使用變量的程序設計語言，因爲函數內部的變量狀態不肯定，一樣的輸入，可能獲得不一樣的輸出，所以，這種函數是有反作用的。

函數式編程的一個特色就是，容許把函數自己做爲參數傳入另外一個函數，還容許返回一個函數！

Python對函數式編程提供部分支持。因爲Python容許使用變量，所以，Python不是純函數式編程語言。

1.高階函數

傳入函數
既然變量能夠指向函數，函數的參數能接收變量，那麼一個函數就能夠接收另外一個函數做爲參數，這種函數就稱之爲高階函數。

一個最簡單的高階函數：

abs
<built-in function abs>
abs(-10)
10
x=abs(-2)
x
2
f=abs
f
<built-in function abs>
f(-2)
2
abs=10
abs
10
abs(-2)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'int' object is not callable

[root@mantisbt01 python]# python
Python 3.6.4 (default, Mar 19 2018, 10:30:22)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-16)] on linux
Type "help", "copyright", "credits" or "license" for more information.

abs(-2)
2
f(-2)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'f' is not defined
f=abs
f(-2)
2
def add(x,y,f):
... return f(x) + f(y)
...
print(add(-5,6,abs))
11

map\reduce

abs(-2)
2
f(-2)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'f' is not defined
f=abs
f(-2)
2
def add(x,y,f):
... return f(x) + f(y)
...
print(add(-5,6,abs))
11

def f(x):
... return x*x
...
r=map(f,[1,2,3,4,5,6,7,8,9])
list(r)
[1, 4, 9, 16, 25, 36, 49, 64, 81]
r
<map object at 0x7fa94a74ce10>

L=[]
for n in [1,2,3,4,5,6,7,8,9]:
... L.append(f(n))
...
print(L)
[1, 4, 9, 16, 25, 36, 49, 64, 81]

from functools import reduce
def add(x,y):
... return x+y
...
reduce(add,[1,3,5,7,9])
25

from functools import reduce
def fn(x,y):
... return x*10+y
...
reduce (fn,[1,3,5,7,9])
13579

from functools import reduce
def fn(x,y):
... return x*10+y
...
def char2num(s):
... digits = {'0':0,'1':1,'2':2,'3':3,'4':4,'5':5,'6':6,'7':7,'8':8,'9':9}
... return digits[s]
...
reduce (fn,map(char2num,'13579'))
13579

整理成一個函數

from functools import reduce
DIGITS = {'0':0,'1':1,'2':2,'3':3,'4':4,'5':5,'6':6,'7':7,'8':8,'9':9}
def str2int(s):
... def fn(x,y):
... return x*10+y
... def char2num(s):
... return DIGITS[s]
... return reduce(fn,map(char2num,s))
...
print(str2int('13579'))
13579

from functools import reduce
DIGTS={'0':0,'1':1,'2':2,'3':3,'4':4,'5':5,'6':6,'7':7,'8':8,'9':9}
def char2sum(s):
... return DIGITS[s]
...
def str2int(s):
... return reduce(lambda x,y:x*10+y,map(char2num,s))
...

str2int('13579')
13579
str2int('1239')
1239

利用map()函數，把用戶輸入的不規範的英文名字，變爲首字母大寫，其餘小寫的規範名字。輸入：['adam', 'LISA', 'barT']，輸出：['Adam', 'Lisa', 'Bart']：

def normalize(name):
... name=name[0].upper()+name[1:].lower()
... return name
...
L1=['adam','LISA','BarT']
Ls=list(map(normalize,L1))
print(Ls)
['Adam', 'Lisa', 'Bart']

def normalize2(name):
... name=name.lower()
... name=name.upper()
... return name
...
L1=['adam','LISA','BarT']
L2=list(map(normalize2,L1))
print(L2)
['ADAM', 'LISA', 'BART']

def normalize3(name):
... return name.capitalize()
...
L2=list(map(normalize3,L1))
print(L2)
['Adam', 'Lisa', 'Bart']
L1=['adam','LISA','BarT']
L2=list(map(normalize3,L1))
print(L2)
['Adam', 'Lisa', 'Bart']

Python提供的sum()函數能夠接受一個list並求和，請編寫一個prod()函數，能夠接受一個list並利用reduce()求積：

def prod(L):
... def fn(x,y):
... return xy
... return reduce(fn,L)
...
print('3579=',prod([3,5,7,9]))
357*9= 945
if prod([3,5,7,9])==945:
... print('測試成功!')
... else:
... print('測試失敗!')
...
測試成功!

利用map和reduce編寫一個str2float函數，把字符串'123.456'轉換成浮點數123.456：

from functools import reduce
def str2float(s):
... def fn(x,y):
... return x*10+y
... n=s.index('.')
... s1=list(map(int,[x for x in s[:n]]))
... s2=list(map(int,[x for x in s[n+1:]]))
... return reduce(fn,s1) + reduce(fn,s2)/10**len(s2)
... print('str2float(\'123.456\') =', str2float('123.456'))
...

print('str2float(\'123.456\') =', str2float('123.456'))
str2float('123.456') = 123.456

if abs(str2float('123.456') - 123.456) < 0.00001:
... print('測試成功!')
... else:
... print('測試失敗!')
...
測試成功!

print('str2float(\'1.43\') =', str2float('1.43'))
str2float('1.43') = 1.43

filter

用filter求素數
計算素數的一個方法是埃氏篩法，它的算法理解起來很是簡單：

首先，列出從2開始的全部天然數，構造一個序列：

2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, ...

取序列的第一個數2，它必定是素數，而後用2把序列的2的倍數篩掉：

3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, ...

取新序列的第一個數3，它必定是素數，而後用3把序列的3的倍數篩掉：

5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, ...

取新序列的第一個數5，而後用5把序列的5的倍數篩掉：

7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, ...

不斷篩下去，就能夠獲得全部的素數。

def is_odd(n):
... return n%2 ==1
...
list(filter(is_odd,[1,2,4,6,9,10]))
[1, 9]
list(filter(is_odd,[1,2,4,5,6,9,10,15]))
[1, 5, 9, 15]

def not_empty(s):
... return s and s.strip()
...
list(filter(not_empty,['A','','B',None,'C',' ']))
['A', 'B', 'C']

def _odd_iter():
... n=1
... while True:
... n=n+2
... yield n
...

def primes():
... yield 2
... it = _odd_iter()
... while True:
... n=next(it)
... yield n
... it=filter(_not_divisible(n),it)
...

for n in primes():
... if n < 1000:
... print(n)
... else:
... break
...
2
3
5
7
11
13
17
19
23
29
31
37
41
43
47
53
59
61
67
71
73
79
83
89
97
101
103
107
109
113
127
131
137
139
149
151
157
163
167
173
179
181
191
193
197
199
211
223
227
229
233
239
241
251
257
263
269
271
277
281
283
293
307
311
313
317
331
337
347
349
353
359
367
373
379
383
389
397
401
409
419
421
431
433
439
443
449
457
461
463
467
479
487
491
499
503
509
521
523
541
547
557
563
569
571
577
587
593
599
601
607
613
617
619
631
641
643
647
653
659
661
673
677
683
691
701
709
719
727
733
739
743
751
757
761
769
773
787
797
809
811
821
823
827
829
839
853
857
859
863
877
881
883
887
907
911
919
929
937
941
947
953
967
971
977
983
991
997

回數是指從左向右讀和從右向左讀都是同樣的數，例如12321，909。請利用filter()篩選出回數：

def is_palindrome(n):
... if str(n)==str(str(n)[::-1]):
... return n
...
out=filter(is_palindrome,range(1,1000))

print('1~1000:',list(out))
1~1000: [1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 22, 33, 44, 55, 66, 77, 88, 99, 101, 111, 121, 131, 141, 151, 161, 171, 181, 191, 202, 212, 222, 232, 242, 252, 262, 272, 282, 292, 303, 313, 323, 333, 343, 353, 363, 373, 383, 393, 404, 414, 424, 434, 444, 454, 464, 474, 484, 494, 505, 515, 525, 535, 545, 555, 565, 575, 585, 595, 606, 616, 626, 636, 646, 656, 666, 676, 686, 696, 707, 717, 727, 737, 747, 757, 767, 777, 787, 797, 808, 818, 828, 838, 848, 858, 868, 878, 888, 898, 909, 919, 929, 939, 949, 959, 969, 979, 989, 999]
out=filter(is_palindrome,range(1,200))
print('1~200:',list(out))
1~200: [1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 22, 33, 44, 55, 66, 77, 88, 99, 101, 111, 121, 131, 141, 151, 161, 171, 181, 191]

貌似不能判斷最後一個元素

out=filter(is_palindrome,1)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'int' object is not iterable
out=filter(is_palindrome,range(1))
print('1:',list(out))
1: []
out=filter(is_palindrome,range(1,2))
print('1:',list(out))
1: [1]
out=filter(is_palindrome,range(1,3))
print('1~3:',list(out))
1~3: [1, 2]
out=filter(is_palindrome,range(1,11))
print('1~3:',list(out))
1~3: [1, 2, 3, 4, 5, 6, 7, 8, 9]
out=filter(is_palindrome,range(1,12))
print('1~3:',list(out))
1~3: [1, 2, 3, 4, 5, 6, 7, 8, 9, 11]

法2

def is_palindrome(n):
... a=list(str(n))
... b=list(str(n))
... b.reverse()
... return a==b
...

out=filter(is_palindrome,range(1,11))
print('1~3:',list(out))
1~3: [1, 2, 3, 4, 5, 6, 7, 8, 9]
out=filter(is_palindrome,range(1,12))
print('1~3:',list(out))
1~3: [1, 2, 3, 4, 5, 6, 7, 8, 9, 11]

a=range(1,5)
a
range(1, 5)
list(a)
[1, 2, 3, 4]

sorted

sorted([2,4,-6,21,9])
[-6, 2, 4, 9, 21]
sorted([2,4,-6,21,-9])
[-9, -6, 2, 4, 21]
sorted([2,4,-6,21,-9,0])
[-9, -6, 0, 2, 4, 21]
sorted([2,4,-6,21,-9,0],key=abs)
[0, 2, 4, -6, -9, 21]
sorted(['Bob','about','Zoo','Credit','kel'])
['Bob', 'Credit', 'Zoo', 'about', 'kel']

sorted(['bob','about','Zoo','Credit'],key=str.lower)
['about', 'bob', 'Credit', 'Zoo']

sorted(['bob','about','Zoo','Credit'],key=str.lower,reverse=True)
['Zoo', 'Credit', 'bob', 'about']

L = [('Bob', 75), ('Adam', 92), ('Bart', 66), ('Lisa', 88)]