在工作中遇到一個小問題，需要將一個 python 的字符串轉(zhuǎn)為字典，比如字符串：

<pre style="margin-top: 0px; margin-bottom: 0px; white-space: pre-wrap; word-wrap: break-word; font-family: &quot;Courier New&quot; !important; font-size: 12px !important;">user_info = '{"name" : "john", "gender" : "male", "age": 28}'</pre>

我們想把它轉(zhuǎn)為下面的字典：

<pre style="margin-top: 0px; margin-bottom: 0px; white-space: pre-wrap; word-wrap: break-word; font-family: &quot;Courier New&quot; !important; font-size: 12px !important;">user_dict = {"name" : "john", "gender" : "male", "age": 28}</pre>

有以下幾種方法：

1、通過 json 來轉(zhuǎn)換

<pre style="margin-top: 0px; margin-bottom: 0px; white-space: pre-wrap; word-wrap: break-word; font-family: &quot;Courier New&quot; !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 進行轉(zhuǎn)換存在一個潛在的問題。

由于 json 語法規(guī)定 數(shù)組或?qū)ο笾械淖址仨毷褂秒p引號，不能使用單引號 (官網(wǎng)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” )，因此下面的轉(zhuǎn)換是錯誤的：

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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}"

由于字符串使用單引號，會導致運行出錯

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、通過 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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通過 eval 進行轉(zhuǎn)換就不存在上面使用 json 進行轉(zhuǎn)換的問題。但是，使用 eval 卻存在安全性的問題，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;"># 讓用戶輸入 user_info

user_info = raw_input('input user info: ') # 輸入 {"name" : "john", "gender" : "male", "age": 28}，沒問題
user_dict = eval(user_info) # 輸入 import('os').system('dir')，user_dict 會列出當前的目錄文件！ # 再輸入一些刪除命令，則可以把整個目錄清空了！
user_dict = eval(user_info)</pre>

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3、通過 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>