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Description:

qscodec 1.0.4

A query string encoding and decoding library for Python.
Ported from qs for JavaScript.

Usage
A simple usage example:
import qs_codec as qs

# Encoding
assert qs.encode({'a': 'b'}) == 'a=b'

# Decoding
assert qs.decode('a=b') == {'a': 'b'}

Decoding

dictionaries
import qs_codec as qs
import typing as t

def decode(
value: t.Optional[t.Union[str, t.Dict[str, t.Any]]],
options: qs.DecodeOptions = qs.DecodeOptions(),
) -> t.Dict[str, t.Any]:
"""Decodes a query string into a Dict[str, Any].

Providing custom DecodeOptions will override the default behavior."""
pass
decode allows you to create nested dicts within your query
strings, by surrounding the name of sub-keys with square brackets
[]. For example, the string 'foo[bar]=baz' converts to:
import qs_codec as qs

assert qs.decode('foo[bar]=baz') == {'foo': {'bar': 'baz'}}
URI encoded strings work too:
import qs_codec as qs

assert qs.decode('a%5Bb%5D=c') == {'a': {'b': 'c'}}
You can also nest your dicts, like 'foo[bar][baz]=foobarbaz':
import qs_codec as qs

assert qs.decode('foo[bar][baz]=foobarbaz') == {'foo': {'bar': {'baz': 'foobarbaz'}}}
By default, when nesting dicts qs will only decode up to 5
children deep. This means if you attempt to decode a string like
'a[b][c][d][e][f][g][h][i]=j' your resulting dict will be:
import qs_codec as qs

assert qs.decode("a[b][c][d][e][f][g][h][i]=j") == {
"a": {"b": {"c": {"d": {"e": {"f": {"[g][h][i]": "j"}}}}}}
}
This depth can be overridden by setting the depth:
import qs_codec as qs

assert qs.decode(
'a[b][c][d][e][f][g][h][i]=j',
qs.DecodeOptions(depth=1),
) == {'a': {'b': {'[c][d][e][f][g][h][i]': 'j'}}}
You can configure decode to throw an error
when parsing nested input beyond this depth using strict_depth (defaults to False):
import qs_codec as qs

try:
qs.decode(
'a[b][c][d][e][f][g][h][i]=j',
qs.DecodeOptions(depth=1, strict_depth=True),
)
except IndexError as e:
assert str(e) == 'Input depth exceeded depth option of 1 and strict_depth is True'
The depth limit helps mitigate abuse when decode is used to parse user
input, and it is recommended to keep it a reasonably small number. strict_depth
adds a layer of protection by throwing a IndexError when the limit is exceeded, allowing you to catch and handle such cases.
For similar reasons, by default decode will only parse up to 1000 parameters. This can be overridden by passing a
parameter_limit option:
import qs_codec as qs

assert qs.decode(
'a=b&c=d',
qs.DecodeOptions(parameter_limit=1),
) == {'a': 'b'}
To bypass the leading question mark, use ignore_query_prefix:
import qs_codec as qs

assert qs.decode(
'?a=b&c=d',
qs.DecodeOptions(ignore_query_prefix=True),
) == {'a': 'b', 'c': 'd'}
An optional delimiter can also be passed:
import qs_codec as qs

assert qs.decode(
'a=b;c=d',
qs.DecodeOptions(delimiter=';'),
) == {'a': 'b', 'c': 'd'}
delimiter can be a regular expression too:
import qs_codec as qs
import re

assert qs.decode(
'a=b;c=d',
qs.DecodeOptions(delimiter=re.compile(r'[;,]')),
) == {'a': 'b', 'c': 'd'}
Option allow_dots
can be used to enable dot notation:
import qs_codec as qs

assert qs.decode(
'a.b=c',
qs.DecodeOptions(allow_dots=True),
) == {'a': {'b': 'c'}}
Option decode_dot_in_keys
can be used to decode dots in keys.
Note: it implies allow_dots, so
decode will error if you set decode_dot_in_keys
to True, and allow_dots to False.
import qs_codec as qs

assert qs.decode(
'name%252Eobj.first=John&name%252Eobj.last=Doe',
qs.DecodeOptions(decode_dot_in_keys=True),
) == {'name.obj': {'first': 'John', 'last': 'Doe'}}
Option allow_empty_lists can
be used to allowing empty list values in a dict
import qs_codec as qs

assert qs.decode(
'foo[]&bar=baz',
qs.DecodeOptions(allow_empty_lists=True),
) == {'foo': [], 'bar': 'baz'}
Option duplicates can be used to
change the behavior when duplicate keys are encountered
import qs_codec as qs

assert qs.decode('foo=bar&foo=baz') == {'foo': ['bar', 'baz']}

assert qs.decode(
'foo=bar&foo=baz',
qs.DecodeOptions(duplicates=qs.Duplicates.COMBINE),
) == {'foo': ['bar', 'baz']}

assert qs.decode(
'foo=bar&foo=baz',
qs.DecodeOptions(duplicates=qs.Duplicates.FIRST),
) == {'foo': 'bar'}

assert qs.decode(
'foo=bar&foo=baz',
qs.DecodeOptions(duplicates=qs.Duplicates.LAST),
) == {'foo': 'baz'}
If you have to deal with legacy browsers or services, there’s also
support for decoding percent-encoded octets as LATIN1:
import qs_codec as qs

assert qs.decode(
'a=%A7',
qs.DecodeOptions(charset=qs.Charset.LATIN1),
) == {'a': '§'}
Some services add an initial utf8=✓ value to forms so that old
Internet Explorer versions are more likely to submit the form as utf-8.
Additionally, the server can check the value against wrong encodings of
the checkmark character and detect that a query string or
application/x-www-form-urlencoded body was not sent as utf-8,
e.g. if the form had an accept-charset parameter or the containing
page had a different character set.
decode supports this mechanism via the
charset_sentinel option.
If specified, the utf8 parameter will be omitted from the returned
dict. It will be used to switch to LATIN1 or
UTF8 mode depending on how the checkmark is encoded.
Important: When you specify both the charset
option and the charset_sentinel option, the
charset will be overridden when the request contains a
utf8 parameter from which the actual charset can be deduced. In that
sense the charset will behave as the default charset
rather than the authoritative charset.
import qs_codec as qs

assert qs.decode(
'utf8=%E2%9C%93&a=%C3%B8',
qs.DecodeOptions(
charset=qs.Charset.LATIN1,
charset_sentinel=True,
),
) == {'a': 'ø'}

assert qs.decode(
'utf8=%26%2310003%3B&a=%F8',
qs.DecodeOptions(
charset=qs.Charset.UTF8,
charset_sentinel=True,
),
) == {'a': 'ø'}
If you want to decode the &#…; syntax to the actual character, you can specify the
interpret_numeric_entities
option as well:
import qs_codec qs qs

assert qs.decode(
'a=%26%239786%3B',
qs.DecodeOptions(
charset=qs.Charset.LATIN1,
interpret_numeric_entities=True,
),
) == {'a': '☺'}
It also works when the charset has been detected in
charset_sentinel mode.

lists
decode can also decode lists using a similar [] notation:
import qs_codec as qs

assert qs.decode('a[]=b&a[]=c') == {'a': ['b', 'c']}
You may specify an index as well:
import qs_codec as qs

assert qs.decode('a[1]=c&a[0]=b') == {'a': ['b', 'c']}
Note that the only difference between an index in a list and a key
in a dict is that the value between the brackets must be a number to
create a list. When creating lists with specific indices,
decode will compact a sparse list to
only the existing values preserving their order:
import qs_codec as qs

assert qs.decode('a[1]=b&a[15]=c') == {'a': ['b', 'c']}
Note that an empty string is also a value, and will be preserved:
import qs_codec as qs

assert qs.decode('a[]=&a[]=b') == {'a': ['', 'b']}

assert qs.decode('a[0]=b&a[1]=&a[2]=c') == {'a': ['b', '', 'c']}
decode will also limit specifying indices
in a list to a maximum index of 20. Any list members with an
index of greater than 20 will instead be converted to a dict with
the index as the key. This is needed to handle cases when someone sent,
for example, a[999999999] and it will take significant time to iterate
over this huge list.
import qs_codec as qs

assert qs.decode('a[100]=b') == {'a': {'100': 'b'}}
This limit can be overridden by passing an list_limit
option:
import qs_codec as qs

assert qs.decode(
'a[1]=b',
qs.DecodeOptions(list_limit=0),
) == {'a': {'1': 'b'}}
To disable list parsing entirely, set parse_lists
to False.
import qs_codec as qs

assert qs.decode(
'a[]=b',
qs.DecodeOptions(parse_lists=False),
) == {'a': {'0': 'b'}}
If you mix notations, decode will merge the two items into a dict:
import qs_codec as qs

assert qs.decode('a[0]=b&a[b]=c') == {'a': {'0': 'b', 'b': 'c'}}
You can also create lists of dicts:
import qs_codec as qs

assert qs.decode('a[][b]=c') == {'a': [{'b': 'c'}]}
(decode cannot convert nested ``dict``s, such as ``’a={b:1},{c:d}’``)

primitive values (int, bool, None, etc.)
By default, all values are parsed as strings.
import qs_codec as qs

assert qs.decode(
'a=15&b=true&c=null',
) == {'a': '15', 'b': 'true', 'c': 'null'}

Encoding
import qs_codec as qs
import typing as t

def encode(
value: t.Any,
options: qs.EncodeOptions = qs.EncodeOptions()
) -> str:
"""Encodes an object into a query string.

Providing custom EncodeOptions will override the default behavior."""
pass
When encoding, encode by default URI encodes output. dicts are
encoded as you would expect:
import qs_codec as qs

assert qs.encode({'a': 'b'}) == 'a=b'
assert qs.encode({'a': {'b': 'c'}}) == 'a%5Bb%5D=c'
This encoding can be disabled by setting the encode
option to False:
import qs_codec as qs

assert qs.encode(
{'a': {'b': 'c'}},
qs.EncodeOptions(encode=False),
) == 'a[b]=c'
Encoding can be disabled for keys by setting the
encode_values_only option to True:
import qs_codec as qs

assert qs.encode(
{
'a': 'b',
'c': ['d', 'e=f'],
'f': [
['g'],
['h']
]
},
qs.EncodeOptions(encode_values_only=True)
) == 'a=b&c[0]=d&c[1]=e%3Df&f[0][0]=g&f[1][0]=h'
This encoding can also be replaced by a custom Callable in the
encoder option:
import qs_codec as qs
import typing as t

def custom_encoder(
value: str,
charset: t.Optional[qs.Charset],
format: t.Optional[qs.Format],
) -> str:
if value == 'č':
return 'c'
return value

assert qs.encode(
{'a': {'b': 'č'}},
qs.EncodeOptions(encoder=custom_encoder),
) == 'a[b]=c'
(Note: the encoder option does not apply if
encode is False).
Similar to encoder there is a
decoder option for decode
to override decoding of properties and values:
import qs_codec as qs,
typing as t

def custom_decoder(
value: t.Any,
charset: t.Optional[qs.Charset],
) -> t.Union[int, str]:
try:
return int(value)
except ValueError:
return value

assert qs.decode(
'foo=123',
qs.DecodeOptions(decoder=custom_decoder),
) == {'foo': 123}
Examples beyond this point will be shown as though the output is not URI
encoded for clarity. Please note that the return values in these cases
will be URI encoded during real usage.
When lists are encoded, they follow the
list_format option, which defaults to
INDICES:
import qs_codec as qs

assert qs.encode(
{'a': ['b', 'c', 'd']},
qs.EncodeOptions(encode=False)
) == 'a[0]=b&a[1]=c&a[2]=d'
You may override this by setting the indices option to
False, or to be more explicit, the list_format
option to REPEAT:
import qs_codec as qs

assert qs.encode(
{'a': ['b', 'c', 'd']},
qs.EncodeOptions(
encode=False,
indices=False,
),
) == 'a=b&a=c&a=d'
You may use the list_format option to specify the
format of the output list:
import qs_codec as qs

# ListFormat.INDICES
assert qs.encode(
{'a': ['b', 'c']},
qs.EncodeOptions(
encode=False,
list_format=qs.ListFormat.INDICES,
),
) == 'a[0]=b&a[1]=c'

# ListFormat.BRACKETS
assert qs.encode(
{'a': ['b', 'c']},
qs.EncodeOptions(
encode=False,
list_format=qs.ListFormat.BRACKETS,
),
) == 'a[]=b&a[]=c'

# ListFormat.REPEAT
assert qs.encode(
{'a': ['b', 'c']},
qs.EncodeOptions(
encode=False,
list_format=qs.ListFormat.REPEAT,
),
) == 'a=b&a=c'

# ListFormat.COMMA
assert qs.encode(
{'a': ['b', 'c']},
qs.EncodeOptions(
encode=False,
list_format=qs.ListFormat.COMMA,
),
) == 'a=b,c'
Note: When using list_format set to
COMMA, you can also pass the
comma_round_trip option set to True or
False, to append [] on single-item lists, so that they can round trip through a decoding.
BRACKETS notation is used for encoding dicts by default:
import qs_codec as qs

assert qs.encode(
{'a': {'b': {'c': 'd', 'e': 'f'}}},
qs.EncodeOptions(encode=False),
) == 'a[b][c]=d&a[b][e]=f'
You may override this to use dot notation by setting the
allow_dots option to True:
import qs_codec as qs

assert qs.encode(
{'a': {'b': {'c': 'd', 'e': 'f'}}},
qs.EncodeOptions(encode=False, allow_dots=True),
) == 'a.b.c=d&a.b.e=f'
You may encode dots in keys of dicts by setting
encode_dot_in_keys to True:
import qs_codec as qs

assert qs.encode(
{'name.obj': {'first': 'John', 'last': 'Doe'}},
qs.EncodeOptions(
allow_dots=True,
encode_dot_in_keys=True,
),
) == 'name%252Eobj.first=John&name%252Eobj.last=Doe'
Caveat: When both encode_values_only
and encode_dot_in_keys are set to
True, only dots in keys and nothing else will be encoded!
You may allow empty list values by setting the
allow_empty_lists option to True:
import qs_codec as qs

assert qs.encode(
{'foo': [], 'bar': 'baz', },
qs.EncodeOptions(
encode=False,
allow_empty_lists=True,
),
) == 'foo[]&bar=baz'
Empty strings and None values will be omitted, but the equals sign (=) remains in place:
import qs_codec as qs

assert qs.encode({'a': ''}) == 'a='
Keys with no values (such as an empty dict or list) will return nothing:
import qs_codec as qs

assert qs.encode({'a': []}) == ''

assert qs.encode({'a': {}}) == ''

assert qs.encode({'a': [{}]}) == ''

assert qs.encode({'a': {'b': []}}) == ''

assert qs.encode({'a': {'b': {}}}) == ''
Undefined properties will be omitted entirely:
import qs_codec as qs

assert qs.encode({'a': None, 'b': qs.Undefined()}) == 'a='
The query string may optionally be prepended with a question mark (?) by setting
add_query_prefix to True:
import qs_codec as qs

assert qs.encode(
{'a': 'b', 'c': 'd'},
qs.EncodeOptions(add_query_prefix=True),
) == '?a=b&c=d'
The delimiter may be overridden as well:
import qs_codec as qs

assert qs.encode(
{'a': 'b', 'c': 'd', },
qs.EncodeOptions(delimiter=';')
) == 'a=b;c=d'
If you only want to override the serialization of datetime
objects, you can provide a Callable in the
serialize_date option:
import qs_codec as qs
import datetime
import sys

# First case: encoding a datetime object to an ISO 8601 string
assert (
qs.encode(
{
"a": (
datetime.datetime.fromtimestamp(7, datetime.UTC)
if sys.version_info.major == 3 and sys.version_info.minor >= 11
else datetime.datetime.utcfromtimestamp(7)
)
},
qs.EncodeOptions(encode=False),
)
== "a=1970-01-01T00:00:07+00:00"
if sys.version_info.major == 3 and sys.version_info.minor >= 11
else "a=1970-01-01T00:00:07"
)

# Second case: encoding a datetime object to a timestamp string
assert (
qs.encode(
{
"a": (
datetime.datetime.fromtimestamp(7, datetime.UTC)
if sys.version_info.major == 3 and sys.version_info.minor >= 11
else datetime.datetime.utcfromtimestamp(7)
)
},
qs.EncodeOptions(encode=False, serialize_date=lambda date: str(int(date.timestamp()))),
)
== "a=7"
)
To affect the order of parameter keys, you can set a Callable in the
sort option:
import qs_codec as qs

assert qs.encode(
{'a': 'c', 'z': 'y', 'b': 'f'},
qs.EncodeOptions(
encode=False,
sort=lambda a, b: (a > b) - (a < b)
)
) == 'a=c&b=f&z=y'
Finally, you can use the filter option to restrict
which keys will be included in the encoded output. If you pass a Callable, it will be called for each key to obtain
the replacement value. Otherwise, if you pass a list, it will be used to select properties and list indices to
be encoded:
import qs_codec as qs
import datetime
import sys

# First case: using a Callable as filter
assert (
qs.encode(
{
"a": "b",
"c": "d",
"e": {
"f": (
datetime.datetime.fromtimestamp(123, datetime.UTC)
if sys.version_info.major == 3 and sys.version_info.minor >= 11
else datetime.datetime.utcfromtimestamp(123)
),
"g": [2],
},
},
qs.EncodeOptions(
encode=False,
filter=lambda prefix, value: {
"b": None,
"e[f]": int(value.timestamp()) if isinstance(value, datetime.datetime) else value,
"e[g][0]": value * 2 if isinstance(value, int) else value,
}.get(prefix, value),
),
)
== "a=b&c=d&e[f]=123&e[g][0]=4"
)

# Second case: using a list as filter
assert qs.encode(
{'a': 'b', 'c': 'd', 'e': 'f'},
qs.EncodeOptions(
encode=False,
filter=['a', 'e']
)
) == 'a=b&e=f'

# Third case: using a list as filter with indices
assert qs.encode(
{
'a': ['b', 'c', 'd'],
'e': 'f',
},
qs.EncodeOptions(
encode=False,
filter=['a', 0, 2]
)
) == 'a[0]=b&a[2]=d'

Handling None values
By default, None values are treated like empty strings:
import qs_codec as qs

assert qs.encode({'a': None, 'b': ''}) == 'a=&b='
To distinguish between None values and empty strs use the
strict_null_handling flag.
In the result string the None values have no = sign:
import qs_codec as qs

assert qs.encode(
{'a': None, 'b': ''},
qs.EncodeOptions(strict_null_handling=True),
) == 'a&b='
To decode values without = back to None use the
strict_null_handling flag:
import qs_codec as qs

assert qs.decode(
'a&b=',
qs.DecodeOptions(strict_null_handling=True),
) == {'a': None, 'b': ''}
To completely skip rendering keys with None values, use the
skip_nulls flag:
import qs_codec as qs

assert qs.encode(
{'a': 'b', 'c': None},
qs.EncodeOptions(skip_nulls=True),
) == 'a=b'
If you’re communicating with legacy systems, you can switch to
LATIN1 using the
charset option:
import qs_codec as qs

assert qs.encode(
{'æ': 'æ'},
qs.EncodeOptions(charset=qs.Charset.LATIN1)
) == '%E6=%E6'
Characters that don’t exist in LATIN1
will be converted to numeric entities, similar to what browsers do:
import qs_codec as qs

assert qs.encode(
{'a': '☺'},
qs.EncodeOptions(charset=qs.Charset.LATIN1)
) == 'a=%26%239786%3B'
You can use the charset_sentinel
option to announce the character by including an utf8=✓ parameter with the proper
encoding of the checkmark, similar to what Ruby on Rails and others do when submitting forms.
import qs_codec as qs

assert qs.encode(
{'a': '☺'},
qs.EncodeOptions(charset_sentinel=True)
) == 'utf8=%E2%9C%93&a=%E2%98%BA'

assert qs.encode(
{'a': 'æ'},
qs.EncodeOptions(charset=qs.Charset.LATIN1, charset_sentinel=True)
) == 'utf8=%26%2310003%3B&a=%E6'

Dealing with special character sets
By default, the encoding and decoding of characters is done in
UTF8, and
LATIN1 support is also built in via
the charset
and charset parameter,
respectively.
If you wish to encode query strings to a different character set (i.e.
Shift JIS)
import qs_codec as qs
import codecs
import typing as t

def custom_encoder(
string: str,
charset: t.Optional[qs.Charset],
format: t.Optional[qs.Format],
) -> str:
if string:
buf: bytes = codecs.encode(string, 'shift_jis')
result: t.List[str] = ['{:02x}'.format(b) for b in buf]
return '%' + '%'.join(result)
return ''

assert qs.encode(
{'a': 'こんにちは！'},
qs.EncodeOptions(encoder=custom_encoder)
) == '%61=%82%b1%82%f1%82%c9%82%bf%82%cd%81%49'
This also works for decoding of query strings:
import qs_codec as qs
import re
import codecs
import typing as t

def custom_decoder(
string: str,
charset: t.Optional[qs.Charset],
) -> t.Optional[str]:
if string:
result: t.List[int] = []
while string:
match: t.Optional[t.Match[str]] = re.search(r'%([0-9A-F]{2})', string, re.IGNORECASE)
if match:
result.append(int(match.group(1), 16))
string = string[match.end():]
else:
break
buf: bytes = bytes(result)
return codecs.decode(buf, 'shift_jis')
return None

assert qs.decode(
'%61=%82%b1%82%f1%82%c9%82%bf%82%cd%81%49',
qs.DecodeOptions(decoder=custom_decoder)
) == {'a': 'こんにちは！'}

RFC 3986 and RFC 1738 space encoding
The default format is
RFC3986 which encodes
' ' to %20 which is backward compatible. You can also set the
format to
RFC1738 which encodes ' ' to +.
import qs_codec as qs

assert qs.encode(
{'a': 'b c'},
qs.EncodeOptions(format=qs.Format.RFC3986)
) == 'a=b%20c'

assert qs.encode(
{'a': 'b c'},
qs.EncodeOptions(format=qs.Format.RFC3986)
) == 'a=b%20c'

assert qs.encode(
{'a': 'b c'},
qs.EncodeOptions(format=qs.Format.RFC1738)
) == 'a=b+c'

Special thanks to the authors of
qs for JavaScript: - Jordan
Harband - TJ
Holowaychuk