函数：递归是神马
递归求阶乘
写一个求阶乘的函数
正整数阶乘指从1乘以2乘以3乘以4一直乘到所要求的数。
例如所给的数是5，则阶乘式是1×2×3×4×5，得到的积是120，所以120就是4的阶乘。
def factorial(n):
result = n
for i in range(1,n):
result *= i
return result
number = int(input("请输入一个正整数:"))
result = factorial(number)
print("%d的阶乘是：%d" % (number,result))
def factorial(n):
if n == 1:
return 1
else:
return n * factorial(n-1)
number = int(input("请输入一个正整数:"))
result = factorial(number)
print("%d的阶乘是：%d" % (number,result))
假设我们n的值传入是5，那么：
factorial(5) = 5 * factorial(4)
factorial(4) = 4 * factorial(3)
factorial(3) = 3 * factorial(2)
factorial(2) = 2 * factorial(1)
factorial(1) = 1
斐波那契数列的迭代实现
我们都知道兔子繁殖能力是惊人的，如下图：
所经过的月数123456789101112
兔子的总对数1123581321345589144
我们可以用数学函数来定义：
1，当n=1
F(n) = 1，当n=2
F(n-1)+F(n-2)，当n>2
课间练习：假设我们需要求出经历了20个月后，总共有多少对小兔崽子？（迭代 vs 递归）
def fab(n):
n1 = 1
n2 = 1
n3 = 1
if n < 1:
print('输入有误！')
return -1
while (n-2) > 0:
n3 = n2 + n1
n1 = n2
n2 = n3
n -= 1
return n3
result = fab(20)
if result != -1:
print('总共有%d对小兔崽子诞生！' % result)
def fab(n):
if n < 1:
print('输入有误！')
return -1
if n == 1 or n == 2:
return 1
else:
return fab(n-1) + fab(n-2)
result = fab(20)
if result != -1:
print('总共有%d对小兔崽子诞生！' % result)
递归：汉诺塔
def hanoi(n, x, y, z):
if n == 1:
print(x, ' --> ', z)
else:
hanoi(n-1, x, z, y) # 将前n-1个盘子从x移动到y上
print(x, ' --> ', z) # 将最底下的最后一个盘子从x移动到z上
hanoi(n-1, y, x, z) # 将y上的n-1个盘子移动到z上
n = int(input('请输入汉诺塔的层数：'))
hanoi(n, 'X', 'Y', 'Z')
字典：当索引不好用时
>>> brand = ['李宁' , '耐克' , '阿迪达斯' , '鱼C工作室']
>>> slogan = ['一切皆有可能' , 'Just do it' , 'Impossible is nothing' , '让编程改变世界']
>>> print('鱼C工作室的口号是：', slogan[brand.index('鱼C工作室')])
鱼C工作室的口号是： 让编程改变世界
>>>
创建和访问字典
>>> dict1 = {'李宁':'一切皆有可能' , '耐克': 'Just do it', '阿迪达斯' :'Impossible is nothing', '鱼C工作室':'让编程改变世界'}
>>> print('鱼C工作室的口号是：',dict1['鱼C工作室'])
鱼C工作室的口号是： 让编程改变世界
>>>
>>> dict2 = {1:'one',2:'two',3:'three'}
>>> dict2[2]
'two'
>>>
>>> help(dict)
Help on class dict in module builtins:
class dict(object)
| dict() -> new empty dictionary
| dict(mapping) -> new dictionary initialized from a mapping object's
| (key, value) pairs
| dict(iterable) -> new dictionary initialized as if via:
| d = {}
| for k, v in iterable:
| d[k] = v
| dict(**kwargs) -> new dictionary initialized with the name=value pairs
| in the keyword argument list. For example: dict(one=1, two=2)
|
| Methods defined here:
|
| __contains__(self, key, /)
| True if D has a key k, else False.
|
| __delitem__(self, key, /)
| Delete self[key].
|
| __eq__(self, value, /)
| Return self==value.
|
| __ge__(self, value, /)
| Return self>=value.
|
| __getattribute__(self, name, /)
| Return getattr(self, name).
|
| __getitem__(...)
| x.__getitem__(y) <==> x[y]
|
| __gt__(self, value, /)
| Return self>value.
|
| __init__(self, /, *args, **kwargs)
| Initialize self. See help(type(self)) for accurate signature.
|
| __iter__(self, /)
| Implement iter(self).
|
| __le__(self, value, /)
| Return self<=value.
|
| __len__(self, /)
| Return len(self).
|
| __lt__(self, value, /)
| Return self<value.
|
| __ne__(self, value, /)
| Return self!=value.
|
| __new__(*args, **kwargs) from builtins.type
| Create and return a new object. See help(type) for accurate signature.
|
| __repr__(self, /)
| Return repr(self).
|
| __setitem__(self, key, value, /)
| Set self[key] to value.
|
| __sizeof__(...)
| D.__sizeof__() -> size of D in memory, in bytes
|
| clear(...)
| D.clear() -> None. Remove all items from D.
|
| copy(...)
| D.copy() -> a shallow copy of D
|
| fromkeys(iterable, value=None, /) from builtins.type
| Returns a new dict with keys from iterable and values equal to value.
|
| get(...)
| D.get(k[,d]) -> D[k] if k in D, else d. d defaults to None.
|
| items(...)
| D.items() -> a set-like object providing a view on D's items
|
| keys(...)
| D.keys() -> a set-like object providing a view on D's keys
|
| pop(...)
| D.pop(k[,d]) -> v, remove specified key and return the corresponding value.
| If key is not found, d is returned if given, otherwise KeyError is raised
|
| popitem(...)
| D.popitem() -> (k, v), remove and return some (key, value) pair as a
| 2-tuple; but raise KeyError if D is empty.
|
| setdefault(...)
| D.setdefault(k[,d]) -> D.get(k,d), also set D[k]=d if k not in D
|
| update(...)
| D.update([E, ]**F) -> None. Update D from dict/iterable E and F.
| If E is present and has a .keys() method, then does: for k in E: D[k] = E[k]
| If E is present and lacks a .keys() method, then does: for k, v in E: D[k] = v
| In either case, this is followed by: for k in F: D[k] = F[k]
|
| values(...)
| D.values() -> an object providing a view on D's values
|
| ----------------------------------------------------------------------
| Data and other attributes defined here:
|
| __hash__ = None
>>>
>>> dict3 = dict((('F',70),('i',105),('s',115),('h',104),('c',67)))
>>> dict3
{'F': 70, 'i': 105, 's': 115, 'h': 104, 'c': 67}
>>>
>>> dict4 = dict(小甲鱼='编程改变世界',JM='加强各方面知识')
>>> dict4
{'小甲鱼': '编程改变世界', 'JM': '加强各方面知识'}
>>>
>>> dict4['JM'] = '学习编程'
>>> dict4
{'小甲鱼': '编程改变世界', 'JM': '学习编程'}
>>>
>>> dict4['小明'] = '网络安全'
>>> dict4
{'小甲鱼': '编程改变世界', 'JM': '学习编程', '小明': '网络安全'}
>>>
>>> dict1.fromkeys((1,2,3))
{1: None, 2: None, 3: None}
>>> dict1.fromkeys((1,2,3),'Number')
{1: 'Number', 2: 'Number', 3: 'Number'}
>>>
>>> dict1.fromkeys((1,2,3),('Number','two','three'))
{1: ('Number', 'two', 'three'), 2: ('Number', 'two', 'three'), 3: ('Number', 'two', 'three')}
>>> dict1 =dict1.fromkeys(range(32),'赞')
>>> dict1
{0: '赞', 1: '赞', 2: '赞', 3: '赞', 4: '赞', 5: '赞', 6: '赞', 7: '赞', 8: '赞', 9: '赞', 10: '赞', 11: '赞', 12: '赞', 13: '赞', 14: '赞', 15: '赞', 16: '赞', 17: '赞', 18: '赞', 19: '赞', 20: '赞', 21: '赞', 22: '赞', 23: '赞', 24: '赞', 25: '赞', 26: '赞', 27: '赞', 28: '赞', 29: '赞', 30: '赞', 31: '赞'}
>>> for eachKey in dict1.keys():
print(eachKey)
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
>>> for eachValue in dict1.values():
print(eachValue)
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
赞
>>>
>>> for eachItem in dict1.items():
print(eachItem)
(0, '赞')
(1, '赞')
(2, '赞')
(3, '赞')
(4, '赞')
(5, '赞')
(6, '赞')
(7, '赞')
(8, '赞')
(9, '赞')
(10, '赞')
(11, '赞')
(12, '赞')
(13, '赞')
(14, '赞')
(15, '赞')
(16, '赞')
(17, '赞')
(18, '赞')
(19, '赞')
(20, '赞')
(21, '赞')
(22, '赞')
(23, '赞')
(24, '赞')
(25, '赞')
(26, '赞')
(27, '赞')
(28, '赞')
(29, '赞')
(30, '赞')
(31, '赞')
>>>
>>> print(dict1[31])
赞
>>> print(dict1[32])
Traceback (most recent call last):
File "<pyshell#54>", line 1, in <module>
print(dict1[32])
KeyError: 32
>>>
>>> dict1.get(32)
>>> print(dict1.get(32))
None
>>>
>>> dict1.get(32,'没有')
'没有'
>>> dict1.get(31,'没有')
'赞'
>>>
>>> 31 in dict1
True
>>> 32 in dict1
False
>>>
>>> dict1
{0: '赞', 1: '赞', 2: '赞', 3: '赞', 4: '赞', 5: '赞', 6: '赞', 7: '赞', 8: '赞', 9: '赞', 10: '赞', 11: '赞', 12: '赞', 13: '赞', 14: '赞', 15: '赞', 16: '赞', 17: '赞', 18: '赞', 19: '赞', 20: '赞', 21: '赞', 22: '赞', 23: '赞', 24: '赞', 25: '赞', 26: '赞', 27: '赞', 28: '赞', 29: '赞', 30: '赞', 31: '赞'}
>>> dict1.clear()
>>> dict1
{}
>>> dict1 = {}
>>> a = {'姓名':'小甲鱼'}
>>> b = a
>>> b
{'姓名': '小甲鱼'}
>>> b
{'姓名': '小甲鱼'}
>>> a = {}
>>> a
{}
>>> b
{'姓名': '小甲鱼'}
>>> a = b
>>> a
{'姓名': '小甲鱼'}
>>> b
{'姓名': '小甲鱼'}
>>> a.clear()
>>> a
{}
>>> b
{}
>>> dir(dict)
['__class__', '__contains__', '__delattr__', '__delitem__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__setitem__', '__sizeof__', '__str__', '__subclasshook__', 'clear', 'copy', 'fromkeys', 'get', 'items', 'keys', 'pop', 'popitem', 'setdefault', 'update', 'values']
>>>
>>> a = {1:'one',2:'two',3:'three'}
>>> b = a.copy()
>>> c = a
>>> c
{1: 'one', 2: 'two', 3: 'three'}
>>> a
{1: 'one', 2: 'two', 3: 'three'}
>>> b
{1: 'one', 2: 'two', 3: 'three'}
>>> id(a)
48459920
>>> id(b)
48463736
>>> id(c)
48459920
>>> c[4] = 'four'
>>> c
{1: 'one', 2: 'two', 3: 'three', 4: 'four'}
>>> a
{1: 'one', 2: 'two', 3: 'three', 4: 'four'}
>>> b
{1: 'one', 2: 'two', 3: 'three'}
>>>
>>> a.pop(2)
'two'
>>> a
{1: 'one', 3: 'three', 4: 'four'}
>>> a.popitem()
(4, 'four')
>>>
>>> a
{1: 'one', 3: 'three'}
>>> a.setdefault('小白')
>>> a
{1: 'one', 3: 'three', '小白': None}
>>> a.setdefault(5,'five')
'five'
>>> a
{1: 'one', 3: 'three', '小白': None, 5: 'five'}
>>>
>>> b = {'小白':'狗'}
>>> a.update(b)
>>> a
{1: 'one', 3: 'three', '小白': '狗', 5: 'five'}
>>>
