Python 入门学习（三）

1 classmate = [‘niu‘,‘meng‘,‘hello world‘] # 中括号表示
2 classmate.append(‘the end‘)
3 classmate.pop()
4 classmate.insert(i,‘insert‘)
5 classmate[0] = ‘change‘
6 classmate = [] len(classmate)=0

1 tuple = (‘hello‘,‘world‘)

1 if <条件判断1>:
2     <执行1>
3 elif <条件判断2>:
4     <执行2>
5 elif <条件判断3>:
6     <执行3>
7 else:
8     <执行4>

1 sum = 0
2 for x in range(101):
3     sum = sum + x
4 print sum

1 >>> d = {‘Michael‘: 95, ‘Bob‘: 75, ‘Tracy‘: 85}
2 >>> d[‘Michael‘]

1 >>> d[‘Thomas‘]
2 Traceback (most recent call last):
3   File "<stdin>", line 1, in <module>
4 KeyError: ‘Thomas‘

1 >>> ‘Thomas‘ in d
2 False

1 >>> d.get(‘Thomas‘)
2 >>> d.get(‘Thomas‘, -1)
3 -1

 1 >>> s = set([1, 2, 3])
 2 >>> s
 3 set([1, 2, 3])
 4 >>> s.add(4) 集合增加一个元素
 5 >>>> s.remove(4) 删除一个元素 
 6 
 7 >>> s1 = set([1, 2, 3])
 8 >>> s2 = set([2, 3, 4])
 9 >>> s1 & s2 求两个集合的交集
10 set([2, 3])
11 >>> s1 | s2
12 set([1, 2, 3, 4])

 1 可变对象list:
 2 >>> a = [‘c‘, ‘b‘, ‘a‘]
 3 >>> a.sort()
 4 >>> a
 5 [‘a‘, ‘b‘, ‘c‘]
 6 
 7 不可变对象：str
 8 >>> a = ‘abc‘
 9 >>> a.replace(‘a‘, ‘A‘)
10 ‘Abc‘
11 >>> a
12 ‘abc‘
13 字符串本身并没有改变

1 def my_abs(x):
2     if x >= 0:
3         return x
4     else:
5         return -x
6 空函数

1 def nop():
2     pass

1 def move(x, y, step, angle=0):
2     nx = x + step * math.cos(angle)
3     ny = y - step * math.sin(angle)
4     return nx, ny
5 
6 >>> r = move(100, 100, 60, math.pi / 6)
7 >>> print r
8 (151.96152422706632, 70.0)

1 def calc(*numbers):
2     sum = 0
3     for n in numbers:
4         sum = sum + n * n
5     return sum

1 def person(name, age, **kw):
2     print ‘name:‘, name, ‘age:‘, age, ‘other:‘, kw 
3 >>> person(‘Bob‘, 35, city=‘Beijing‘)
4 name: Bob age: 35 other: {‘city‘: ‘Beijing‘}
5 >>> person(‘Adam‘, 45, gender=‘M‘, job=‘Engineer‘)
6 name: Adam age: 45 other: {‘gender‘: ‘M‘, ‘job‘: ‘Engineer‘}

1 >>> d = {‘a‘: 1, ‘b‘: 2, ‘c‘: 3}
2 >>> for key in d:
3 ...     print key
4 默认情况下，dict迭代的是key。
5 如果要迭代value，可以用for value in d.itervalues()。
6 如果要同时迭代key和value，可以用for k, v in d.iteritems()。

1 >>> from collections import Iterable
2 >>> isinstance(‘abc‘, Iterable) # str是否可迭代
3 True
4 >>> isinstance([1,2,3], Iterable) # list是否可迭代
5 True
6 >>> isinstance(123, Iterable) # 整数是否可迭代
7 False

1 >>> for i, value in enumerate([‘A‘, ‘B‘, ‘C‘]):
2 ...     print i, value
3 ...
4 0 A
5 1 B
6 2 C

1 >>> for x, y in [(1, 1)print x, y
2 ...
3 1 1
4 2 4
5 3 9

1 >>> range(1, 11)
2 [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
3 >>> [x * x for x in range(1, 11) if x % 2 == 0]
4 >>> [m + n for m in ‘ABC‘ for n in ‘XYZ‘]

1 >>> L = [x * x for x in range(10)]
2 >>> L
3 [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
4 >>> g = (x * x for x in range(10))
5 >>> g
6 <generator object <genexpr> at 0x104feab40>

1 >>> g.next()
2 0
3 >>> g.next()
4 1
5 >>> g = (x * x for x in range(10))
6 >>> for n in g:
7 ...     print n，‘还是使用for循环迭代生成器方便地多呀’

1 def fib(max):
2     n, a, b = 0, 0, 1
3     while n < max:
4         print b
5         a, b = b, a + b
6         n = n + 1

1 print b --> yield b 

1 for i in fib(6): print i