JMESPath (pronounced \ˈjāmz path\) allows you to declaratively specify how to
extract elements from a JSON document.
For example, given this document:
{"foo": {"bar": "baz"}}
The jmespath expression foo.bar will return "baz".
JMESPath also supports:
Referencing elements in a list. Given the data:
{"foo": {"bar": ["one", "two"]}}
The expression: foo.bar[0] will return "one".
You can also reference all the items in a list using the *
syntax:
{"foo": {"bar": [{"name": "one"}, {"name": "two"}]}}
The expression: foo.bar[*].name will return ["one", "two"].
Negative indexing is also supported (-1 refers to the last element
in the list). Given the data above, the expression
foo.bar[-1].name will return "two".
The * can also be used for hash types:
{"foo": {"bar": {"name": "one"}, "baz": {"name": "two"}}}
The expression: foo.*.name will return ["one", "two"].
The grammar is specified using ABNF, as described in RFC4234. You can find the most up to date grammar for JMESPath here.
You can read the full JMESPath specification here.
If you'd like to learn more about the JMESPath language, you can check out the JMESPath tutorial.
In addition to the unit tests for the jmespath modules,
there is a tests/compliance directory that contains
.json files with test cases. This allows other implementations
to verify they are producing the correct output. Each json
file is grouped by feature.
The included python implementation has two convenience functions
that operate on python data structures. You can use search
and give it the jmespath expression and the data:
>>> import jmespath
>>> path = jmespath.search('foo.bar', {'foo': {'bar': 'baz'}})
'baz'
Similar to the re module, you can store the compiled expressions
and reuse them to perform repeated searches:
>>> import jmespath
>>> path = jmespath.compile('foo.bar')
>>> path.search({'foo': {'bar': 'baz'}})
'baz'
>>> path.search({'foo': {'bar': 'other'}})
'other'
You can also use the jmespath.parser.Parser class directly
if you want more control.