Request Parsing¶
Flask-RESTful’s request parsing interface, reqparse
, is modeled after
the argparse interface.
It’s designed to provide simple and uniform access to any variable on the
flask.request
object in Flask.
Basic Arguments¶
Here’s a simple example of the request parser. It looks for two arguments in
the flask.Request.values
dict: an integer and a string
from flask_restful import reqparse
parser = reqparse.RequestParser()
parser.add_argument('rate', type=int, help='Rate cannot be converted')
parser.add_argument('name')
args = parser.parse_args()
Note
The default argument type is a unicode string. This will be str
in
python3 and unicode
in python2.
If you specify the help
value, it will be rendered as the error message
when a type error is raised while parsing it. If you do not specify a help
message, the default behavior is to return the message from the type error
itself.
By default, arguments are not required. Also, arguments supplied in the request that are not part of the RequestParser will be ignored.
Also note: Arguments declared in your request parser but not set in
the request itself will default to None
.
Required Arguments¶
To require a value be passed for an argument, just add required=True
to
the call to add_argument()
.
parser.add_argument('name', required=True,
help="Name cannot be blank!")
Multiple Values & Lists¶
If you want to accept multiple values for a key as a list, you can pass
action='append'
parser.add_argument('name', action='append')
This will let you make queries like
curl http://api.example.com -d "name=bob" -d "name=sue" -d "name=joe"
And your args will look like this
args = parser.parse_args()
args['name'] # ['bob', 'sue', 'joe']
Other Destinations¶
If for some reason you’d like your argument stored under a different name once
it’s parsed, you can use the dest
keyword argument.
parser.add_argument('name', dest='public_name')
args = parser.parse_args()
args['public_name']
Argument Locations¶
By default, the RequestParser
tries to parse values from
flask.Request.values
, and flask.Request.json
.
Use the location
argument to add_argument()
to specify alternate locations to pull the values from. Any variable on the
flask.Request
can be used. For example:
# Look only in the POST body
parser.add_argument('name', type=int, location='form')
# Look only in the querystring
parser.add_argument('PageSize', type=int, location='args')
# From the request headers
parser.add_argument('User-Agent', location='headers')
# From http cookies
parser.add_argument('session_id', location='cookies')
# From file uploads
parser.add_argument('picture', type=werkzeug.datastructures.FileStorage, location='files')
Multiple Locations¶
Multiple argument locations can be specified by passing a list to location
:
parser.add_argument('text', location=['headers', 'values'])
The last location
listed takes precedence in the result set.
Parser Inheritance¶
Often you will make a different parser for each resource you write. The problem
with this is if parsers have arguments in common. Instead of rewriting
arguments you can write a parent parser containing all the shared arguments and
then extend the parser with copy()
. You can
also overwrite any argument in the parent with
replace_argument()
, or remove it completely
with remove_argument()
. For example:
from flask_restful import reqparse
parser = reqparse.RequestParser()
parser.add_argument('foo', type=int)
parser_copy = parser.copy()
parser_copy.add_argument('bar', type=int)
# parser_copy has both 'foo' and 'bar'
parser_copy.replace_argument('foo', required=True, location='json')
# 'foo' is now a required str located in json, not an int as defined
# by original parser
parser_copy.remove_argument('foo')
# parser_copy no longer has 'foo' argument
Error Handling¶
The default way errors are handled by the RequestParser is to abort on the
first error that occurred. This can be beneficial when you have arguments that
might take some time to process. However, often it is nice to have the errors
bundled together and sent back to the client all at once. This behavior can be
specified either at the Flask application level or on the specific
RequestParser instance. To invoke a RequestParser with the bundling errors
option, pass in the argument bundle_errors
. For example
from flask_restful import reqparse
parser = reqparse.RequestParser(bundle_errors=True)
parser.add_argument('foo', type=int, required=True)
parser.add_argument('bar', type=int, required=True)
# If a request comes in not containing both 'foo' and 'bar', the error that
# will come back will look something like this.
{
"message": {
"foo": "foo error message",
"bar": "bar error message"
}
}
# The default behavior would only return the first error
parser = RequestParser()
parser.add_argument('foo', type=int, required=True)
parser.add_argument('bar', type=int, required=True)
{
"message": {
"foo": "foo error message"
}
}
The application configuration key is “BUNDLE_ERRORS”. For example
from flask import Flask
app = Flask(__name__)
app.config['BUNDLE_ERRORS'] = True
Warning
BUNDLE_ERRORS
is a global setting that overrides the bundle_errors
option in individual RequestParser
instances.