在工作中遇到一个小问题，需要将一个 python 的字符串转为字典，比如字符串：
<pre style="margin-top: 0px; margin-bottom: 0px; white-space: pre-wrap; word-wrap: break-word; font-family: "Courier New" !important; font-size: 12px !important;">user_info = '{"name" : "john", "gender" : "male", "age": 28}'</pre>
我们想把它转为下面的字典：
<pre style="margin-top: 0px; margin-bottom: 0px; white-space: pre-wrap; word-wrap: break-word; font-family: "Courier New" !important; font-size: 12px !important;">user_dict = {"name" : "john", "gender" : "male", "age": 28}</pre>
有以下几种方法：
1、通过 json 来转换
<pre style="margin-top: 0px; margin-bottom: 0px; white-space: pre-wrap; word-wrap: break-word; font-family: "Courier New" !important; font-size: 12px !important;">>>> import json >>> user_info= '{"name" : "john", "gender" : "male", "age": 28}'
>>> user_dict = json.loads(user_info) >>> user_dict
{u'gender': u'male', u'age': 28, u'name': u'john'}</pre>
但是使用 json 进行转换存在一个潜在的问题。
由于 json 语法规定 数组或对象之中的字符串必须使用双引号，不能使用单引号 (官网上有一段描述是 “A string is a sequence of zero or more Unicode characters, wrapped in double quotes, using backslash escapes” )，因此下面的转换是错误的：
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<pre style="margin-top: 0px; margin-bottom: 0px; white-space: pre-wrap; word-wrap: break-word; font-family: "Courier New" !important; font-size: 12px !important;">>>> import json >>> user_info = "{'name' : 'john', 'gender' : 'male', 'age': 28}"
由于字符串使用单引号，会导致运行出错
[user_dict = json.loads(user_info)
Traceback (most recent call last):
File "<stdin>", line 1, in <module> File "/usr/local/Cellar/python/2.7.11/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/init.py", line 339, in loads return _default_decoder.decode(s)
File "/usr/local/Cellar/python/2.7.11/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/decoder.py", line 364, in decode
obj, end = self.raw_decode(s, idx=_w(s, 0).end())
File "/usr/local/Cellar/python/2.7.11/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/decoder.py", line 380, in raw_decode
obj, end = self.scan_once(s, idx)
ValueError: Expecting property name: line 1 column 2 (char 1)</pre>
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2、通过 eval
[
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<pre style="margin-top: 0px; margin-bottom: 0px; white-space: pre-wrap; word-wrap: break-word; font-family: "Courier New" !important; font-size: 12px !important;">>>> user_info = '{"name" : "john", "gender" : "male", "age": 28}'
[user_dict = eval(user_info) >>> user_dict
{'gender': 'male', 'age': 28, 'name': 'john'} >>> user_info = "{'name' : 'john', 'gender' : 'male', 'age': 28}"
user_dict = eval(user_info) >>> user_dict
{'gender': 'male', 'age': 28, 'name': 'john'}</pre>
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通过 eval 进行转换就不存在上面使用 json 进行转换的问题。但是，使用 eval 却存在安全性的问题，比如下面的例子:
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<pre style="margin-top: 0px; margin-bottom: 0px; white-space: pre-wrap; word-wrap: break-word; font-family: "Courier New" !important; font-size: 12px !important;"># 让用户输入 user_info
[user_info = raw_input('input user info: ') # 输入 {"name" : "john", "gender" : "male", "age": 28}，没问题
user_dict = eval(user_info) # 输入 import('os').system('dir')，user_dict 会列出当前的目录文件！ # 再输入一些删除命令，则可以把整个目录清空了！
user_dict = eval(user_info)</pre>
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3、通过 literal_eval
[
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<pre style="margin-top: 0px; margin-bottom: 0px; white-space: pre-wrap; word-wrap: break-word; font-family: "Courier New" !important; font-size: 12px !important;">>>> import ast >>> user = '{"name" : "john", "gender" : "male", "age": 28}'
user_dict = ast.literal_eval(user) >>> user_dict
{'gender': 'male', 'age': 28, 'name': 'john'}
user_info = "{'name' : 'john', 'gender' : 'male', 'age': 28}"
user_dict = ast.literal_eval(user) >>> user_dict
{'gender': 'male', 'age': 28, 'name': 'john'}</pre>
