本教程参考网上的一些资料,如有侵权,请联系删除
list是一种有序的集合,可以随时添加和删除其中的元素。 列表的表示形式如下
c = ['A', 'B', 'C']
print c #输出['A', 'B', 'C']
len(c)
c[0],c[1]
c[-1]
,倒数第二个类推c[-2]
c.append('D')
print c #输出['A', 'B', 'C','D']
c.insert(1, 'E')
print c #输出['A', 'E', 'B', 'C', 'D']
c.pop()
print c #输出['A', 'E', 'B', 'C']
c[1]='F'
print c #输出['A', 'F', 'B', 'C']
c=['A',1,True]
tuple称为元组,和list非常类似,但是tuple一旦初始化就不能修改,比如
c=('A','B','C')
现在,c这个tuple不能变了,它没有append(),insert()这样的方法。但你可以使用c[0]
,c[-1]
,但不能赋值成另外的元素。
因为tuple不可变,所以代码更安全。如果可能,能用tuple代替list就尽量用tuple。
如果要定义一个空的tuple,可以写成()
:
>>> a = ()
>>> a
()
但是,要定义一个只有1个元素的tuple,如果你这么定义:a = (5)
,这样只是定义了5,而不是tuple,正确定义应该为a=(5,)
字典用来储存(键, 值)对。你可以这样使用它:
d = {'cat': 'cute', 'dog': 'furry'} # 新建字典
print d['cat'] # 通过key(cat)访问; prints "cute"
print 'cat' in d # 判断字典中是否有key; prints "True"
d['fish'] = 'wet' # 向字典加入对
print d['fish'] # Prints "wet"
# print d['monkey'] # KeyError: 'monkey' not a key of d
print d.get('monkey', 'N/A') # Get an element with a default; prints "N/A"
print d.get('fish', 'N/A') # Get an element with a default; prints "wet"
del d['fish'] # 从字典中移除对
print d.get('fish', 'N/A') # "fish" 不再是key了; prints "N/A"
#循环Loops:在字典中,用键来迭代更加容易。
d = {'person': 2, 'cat': 4, 'spider': 8}
for animal in d:
legs = d[animal]
print 'A %s has %d legs' % (animal, legs)
# Prints "A person has 2 legs", "A spider has 8 legs", "A cat has 4 legs"
#如果你想要访问键和对应的值,那就使用iteritems方法:
d = {'person': 2, 'cat': 4, 'spider': 8}
for animal, legs in d.iteritems():
print 'A %s has %d legs' % (animal, legs)
# Prints "A person has 2 legs", "A spider has 8 legs", "A cat has 4 legs"
#字典推导Dictionary comprehensions:和列表推导类似,但是允许你方便地构建字典。
nums = [0, 1, 2, 3, 4]
even_num_to_square = {x: x ** 2 for x in nums if x % 2 == 0}
print even_num_to_square # Prints "{0: 0, 2: 4, 4: 16}"
python中切片是一个非常好用的功能,下面从代码说明它的用处
c=['ABCD','ABDE']
print c # 输出['ABC', 'ABD']
print c[0][2:] #输出CD
nums = range(5) #nums = [0, 1, 2, 3, 4]
print nums[2:4] # prints "[2, 3]"
print nums[2:] # prints "[2, 3, 4]"
print nums[:2] # prints "[0, 1]"
print nums[:] # prints "[0, 1, 2, 3, 4]"
print nums[:-1] # prints "[0, 1, 2, 3]"
nums[2:4] = [8, 9]
print nums # Prints "[0, 1, 8, 9, 4]"
animals = ['cat', 'dog', 'monkey']
for animal in animals:
print animal
# Prints "cat", "dog", "monkey", each on its own line.
#如果想要在循环体内访问每个元素的指针,可以使用内置的enumerate函数
animals = ['cat', 'dog', 'monkey']
for idx, animal in enumerate(animals):
print '#%d: %s' % (idx + 1, animal)
# Prints "#1: cat", "#2: dog", "#3: monkey", each on its own line
nums = [0, 1, 2, 3, 4]
squares = [x ** 2 for x in nums]
print squares # Prints [0, 1, 4, 9, 16]
#列表推导还可以包含条件:
nums = [0, 1, 2, 3, 4]
even_squares = [x ** 2 for x in nums if x % 2 == 0]
print even_squares # Prints "[0, 4, 16]"