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Python json module usage examples

高洛峰
高洛峰Original
2017-01-13 13:14:181181browse

In fact, JSON is the string representation of a Python dictionary, but as a complex object, the dictionary cannot be transferred directly, so it needs to be converted into a string form. The conversion process is also a serialization process.

Use json.dumps to serialize into json string format 

>>> import json
>>> dic {'Connection': ['keep-alive'], 'Host': ['127.0.0.1:5000'], 'Cache-Control': ['max-age=0']}
>>> jdict = json.dumps({'Connection': ['keep-alive'], 'Host': ['127.0.0.1:5000'], 'Cache-Control': ['max-age=0']})
>>> print jdict
{"Connection": ["keep-alive"], "Host": ["127.0.0.1:5000"], "Cache-Control": ["max-age=0"]}

Although the strings printed by dic and jdict are the same, their actual types are different. dic is a dictionary type and jdict is a string Type

<type &#39;dict&#39;>
>>> type(jdic)
>>> type(jdict)
<type &#39;str&#39;>

You can use json.dumps to serialize the list into json string format

>>> list = [1, 4, 3, 2, 5] 
>>> jlist = json.dumps(list)
>>> print jlist
[1, 4, 3, 2, 5]

list and jlist types are also different

>>> type(list)
<type &#39;list&#39;>
>>> type(jlist)
<type &#39;str&#39;>

json.dumps has the following Parameters 

json.dumps(obj, skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=True, cls=None, indent=None, separators=None, encoding="utf-8", default=None, sort_keys=False, **kw)

key sorting

>>> print json.dumps({1:&#39;a&#39;, 4:&#39;b&#39;, 3:&#39;c&#39;, 2:&#39;d&#39;, 5:&#39;f&#39;},sort_keys=True)
{"1": "a", "2": "d", "3": "c", "4": "b", "5": "f"}

Format alignment

>>> print json.dumps({&#39;4&#39;: 5, &#39;6&#39;: 7}, sort_keys=True, indent=4)
{
    "4": 5, 
    "6": 7
}

Specify delimiter

>>> json.dumps([1,2,3,{&#39;4&#39;: 5, &#39;6&#39;: 7}], separators=(&#39;,&#39;,&#39;:&#39;))
&#39;[1,2,3,{"4":5,"6":7}]&#39;

Use json.dump to serialize into a file object 

>>> json.dump({&#39;4&#39;: 5, &#39;6&#39;: 7}, open(&#39;savejson.txt&#39;, &#39;w&#39;))
>>> print open(&#39;savejson.txt&#39;).readlines()
[&#39;{"4": 5, "6": 7}&#39;]

json.dump parameters are similar to json.dumps

json.dump(obj, fp, skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=True, cls=None, indent=None, separators=None, encoding="utf-8", default=None, sort_keys=False, **kw)

json.loads deserializes json strings into python objects

The function signature is:

json.loads(s[, encoding[, cls[, object_hook[, parse_float[, parse_int[, parse_constant[, object_pairs_hook[, **kw]]]]]]]])

Note that the "s" here must be a string, which will be a unicode character after deserialization 

>>> dobj = json.loads(&#39;{"name":"aaa", "age":18}&#39;)
>>> type(dobj)
<type &#39;dict&#39;>
>>> print dobj
{u&#39;age&#39;: 18, u&#39;name&#39;: u&#39;aaa&#39;}

json.load is deserialized from the file into a python object

The signature is:

json.load(fp[, encoding[, cls[, object_hook[, parse_float[, parse_int[, parse_constant[, object_pairs_hook[, **kw]]]]]]]])

Examples:

>>> fobj = json.load(open(&#39;savejson.txt&#39;))
>>> print fobj
{u&#39;4&#39;: 5, u&#39;6&#39;: 7}
>>> type(fobj)
<type &#39;dict&#39;>

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