Convert a String into python list that is already in list format

Question

i have users emails stored in database like this below.

['[email protected]','[email protected]','[email protected]']

I have to get each email of all users one by one. After querying i wrote the following code.

    cur.execute("sql query")
                rows = cur.fetchall()
                for row in rows:
                    print row[2]
                    print type(row[2])
                    emails = json.loads(json.dumps(row[2]))
                    print type(emails)

<type 'str'>
<type 'unicode'>

it converts it into Unicode instead of list.

the sql query returns a list of records, i also checked it by print row[2] and it prints all the list of emails as i show above. you can see in code that it says it is string. — Muhammad Taqi
– Muhammad Taqi, Commented Mar 20, 2015 at 12:48
In any case, json.dumps() then json.loads() is not going to work, even if the row contained some kind of JSON data. — Martijn Pieters
– Martijn Pieters, Commented Mar 20, 2015 at 12:56
@MTaqi: using json.dumps(something) produces a JSON encoding of something, which you then decode again with json.loads(). You just encoded to JSON and that encoding was then decoded again. The only thing that achieves is that you test if a string can be JSON encoded (it can) and the result is a Unicode string with the same contents as what you started with. — Martijn Pieters
– Martijn Pieters, Commented Mar 20, 2015 at 13:04

unutbu · Accepted Answer · 2015-03-20 12:48:41Z

2

Your row[2] is a string. To convert it to a list you could use ast.literal_eval:

In [29]: text = "['[email protected]','[email protected]','[email protected]']"

In [30]: import ast

In [31]: ast.literal_eval(text)
Out[31]: ['[email protected]', '[email protected]', '[email protected]']

In [32]: type(ast.literal_eval(text))
Out[32]: list

answered Mar 20, 2015 at 12:48

unutbu

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4 Comments

Martijn Pieters Over a year ago

There is no list being built. The OP is converting each email address to JSON and back.

unutbu Over a year ago

He shows print row[2] prints ['[email protected]','[email protected]','[email protected]']. Notice there are three print statements, and three lines of output.

Martijn Pieters Over a year ago

I am not convinced that that's the case. Also, some databases allow for JSON results in a column that is then decoded when querying. See initd.org/psycopg/docs/extras.html#json-adaptation for example.

Martijn Pieters Over a year ago

And the print statements in the code don't match up with the output produced below the code. The list at the top of the answer is not necessarily one such row[2] being printed.

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