python字典（dictionary）使用：不常用的基本函数例子

Operation Result Notes len(a) the number of items in a 得到字典中元素的个数   a[k] the item of a with key k 取得键K所对应的值 (1), (10) a[k] = v set a[k] to v 设定键k所对应的值成为v   del a[k] remove a[k] from a 从字典中删除键为k的元素 (1) a.clear() remove all items from a 清空整个字典   a.copy() a (shallow) copy of a 得到字典副本   k in a True if a has a key k, else False 字典中存在键k则为返回True，没有则返回False (2) k not in a Equivalent to not k in a   字典中不存在键k则为返回true,反之返回False (2) a.has_key(k) Equivalent to k in a, use that form in new code 等价于k in a   a.items() a copy of a‘s list of (key, value) pairs 得到一个键，值的list (3) a.keys() a copy of a‘s list of keys 得到键的list (3) a.update([b]) updates (and overwrites) key/value pairs from b从b字典中更新a字典，如果键相同则更新，a中不存在则追加 (9) a.fromkeys(seq[, value]) Creates a new dictionary with keys from seq and values set to value  (7) a.values() a copy of a‘s list of values (3) a.get(k[, x]) a[k] if k in a, else x (4) a.setdefault(k[, x]) a[k] if k in a, else x (also setting it) (5) a.pop(k[, x]) a[k] if k in a, else x (and remove k) (8) a.popitem() remove and return an arbitrary (key, value) pair (6) a.iteritems() return an iterator over (key, value) pairs (2), (3) a.iterkeys() return an iterator over the mapping‘s keys (2), (3) a.itervalues() return an iterator over the mapping‘s values (2), (3)

测试code：

[wizad@sr104 lmj]$ vim test.py   
dict = {"a" : "apple", "b" : "banana", "g" : "grape", "o" : "orange"}
for k in dict:
  print "dict[%s]="%k,dict[k]


key="c"
if "c" not in dict:
  print "it is not in %s" %key


print "-------------"
print dict.items()
print dict.keys()
print dict.values()


print "-------------"
iter = dict.iteritems()
for it in iter:
  print "iteritems is:",it
  print type(it)


print "-------------"
key_iter = dict.iterkeys()
for ki in key_iter:
  print "key_iter is",ki
  print type(ki)


print "-------------"
val_iter = dict.itervalues()
for vi in val_iter:
  print "val_iter is",vi
  print type(vi)
print "-------------"

结果：

dict[a]= apple
dict[b]= banana
dict[o]= orange
dict[g]= grape
it is not in c
-------------
[(‘a‘, ‘apple‘), (‘b‘, ‘banana‘), (‘o‘, ‘orange‘), (‘g‘, ‘grape‘)]
[‘a‘, ‘b‘, ‘o‘, ‘g‘]
[‘apple‘, ‘banana‘, ‘orange‘, ‘grape‘]
-------------
iteritems is: (‘a‘, ‘apple‘)
<type ‘tuple‘>
iteritems is: (‘b‘, ‘banana‘)
<type ‘tuple‘>
iteritems is: (‘o‘, ‘orange‘)
<type ‘tuple‘>
iteritems is: (‘g‘, ‘grape‘)
<type ‘tuple‘>
-------------
key_iter is a
<type ‘str‘>
key_iter is b
<type ‘str‘>
key_iter is o
<type ‘str‘>
key_iter is g
<type ‘str‘>
-------------
val_iter is apple
<type ‘str‘>
val_iter is banana
<type ‘str‘>
val_iter is orange
<type ‘str‘>
val_iter is grape
<type ‘str‘>
-------------

此外还有：

#字典的update：合并两个字典，无序
dict = {"a" : "apple", "b" : "banana"}
print dict
dict2 = {"c" : "grape", "d" : "orange"}
dict.update(dict2)
print dict
#udpate()的等价语句
D = {"key1" : "value1", "key2" : "value2"}
E = {"key3" : "value3", "key4" : "value4"}
for k in E:
    D[k] = E[k]
print D

输出：

{‘key3‘: ‘value3‘, ‘key2‘: ‘value2‘, ‘key1‘: ‘value1‘, ‘key4‘: ‘value4‘}

#设置默认值

dict = {}
dict.setdefault("a")
print dict
dict["a"] = "apple"
dict.setdefault("a","default")
print dict

#调用sorted()排序
dict = {"a" : "apple", "b" : "grape", "c" : "orange", "d" : "banana"}
print dict  
#按照key排序 
print sorted(dict.items(), key=lambda d: d[0])
#按照value排序 
print sorted(dict.items(), key=lambda d: d[1])

#字典的浅拷贝
dict = {"a" : "apple", "b" : "grape"}
dict2 = {"c" : "orange", "d" : "banana"}
dict2 = dict.copy()
print dict2

#字典的深拷贝
import copy
dict = {"a" : "apple", "b" : {"g" : "grape","o" : "orange"}}
dict2 = copy.deepcopy(dict)
dict3 = copy.copy(dict)
dict2["b"]["g"] = "orange"
print dict
dict3["b"]["g"] = "orange"
print dict