Utilities

Various utility functions shipped with Werkzeug.

HTML Helpers

class werkzeug.utils.HTMLBuilder(dialect)

Helper object for HTML generation.

Per default there are two instances of that class. The html one, and the xhtml one for those two dialects. The class uses keyword parameters and positional parameters to generate small snippets of HTML.

Keyword parameters are converted to XML/SGML attributes, positional arguments are used as children. Because Python accepts positional arguments before keyword arguments it’s a good idea to use a list with the star-syntax for some children:

>>> html.p(class_='foo', *[html.a('foo', href='foo.html'), ' ',
...                        html.a('bar', href='bar.html')])
'<p class="foo"><a href="foo.html">foo</a> <a href="bar.html">bar</a></p>'

This class works around some browser limitations and can not be used for arbitrary SGML/XML generation. For that purpose lxml and similar libraries exist.

Calling the builder escapes the string passed:

>>> html.p(html("<foo>"))
'<p>&lt;foo&gt;</p>'

Deprecated since version 2.0: Will be removed in Werkzeug 2.1.

werkzeug.utils.escape(s)

Replace &, <, >, ", and ' with HTML-safe sequences.

None is escaped to an empty string.

Deprecated since version 2.0: Will be removed in Werkzeug 2.1. Use MarkupSafe instead.

Parameters: s (Any) –
Return type: str

werkzeug.utils.unescape(s)

The reverse of escape(). This unescapes all the HTML entities, not only those inserted by escape.

Deprecated since version 2.0: Will be removed in Werkzeug 2.1. Use MarkupSafe instead.

Parameters: s (str) –
Return type: str

General Helpers

class werkzeug.utils.cached_property(fget, name=None, doc=None)

A property() that is only evaluated once. Subsequent access returns the cached value. Setting the property sets the cached value. Deleting the property clears the cached value, accessing it again will evaluate it again.

class Example:
    @cached_property
    def value(self):
        # calculate something important here
        return 42

e = Example()
e.value  # evaluates
e.value  # uses cache
e.value = 16  # sets cache
del e.value  # clears cache

The class must have a __dict__ for this to work.

Changed in version 2.0: del obj.name clears the cached value.

Parameters

fget (Callable[[Any], Any]) –
name (Optional[str]) –
doc (Optional[str]) –

Return type

None

werkzeug.utils.invalidate_cached_property(obj, name)

Invalidates the cache for a cached_property:

>>> class Test(object):
...     @cached_property
...     def magic_number(self):
...         print("recalculating...")
...         return 42
...
>>> var = Test()
>>> var.magic_number
recalculating...
42
>>> var.magic_number
42
>>> invalidate_cached_property(var, "magic_number")
>>> var.magic_number
recalculating...
42

You must pass the name of the cached property as the second argument.

Deprecated since version 2.0: Will be removed in Werkzeug 2.1. Use del obj.name instead.

Parameters

obj (object) –
name (str) –

Return type

None

class werkzeug.utils.environ_property(name, default=None, load_func=None, dump_func=None, read_only=None, doc=None)

Maps request attributes to environment variables. This works not only for the Werkzeug request object, but also any other class with an environ attribute:

>>> class Test(object):
...     environ = {'key': 'value'}
...     test = environ_property('key')
>>> var = Test()
>>> var.test
'value'

If you pass it a second value it’s used as default if the key does not exist, the third one can be a converter that takes a value and converts it. If it raises ValueError or TypeError the default value is used. If no default value is provided None is used.

Per default the property is read only. You have to explicitly enable it by passing read_only=False to the constructor.

class werkzeug.utils.header_property(name, default=None, load_func=None, dump_func=None, read_only=None, doc=None): Like environ_property but for headers.

werkzeug.utils.redirect(location, code=302, Response=None)

Returns a response object (a WSGI application) that, if called, redirects the client to the target location. Supported codes are 301, 302, 303, 305, 307, and 308. 300 is not supported because it’s not a real redirect and 304 because it’s the answer for a request with a request with defined If-Modified-Since headers.

Changelog

New in version 0.10: The class used for the Response object can now be passed in.

New in version 0.6: The location can now be a unicode string that is encoded using the iri_to_uri() function.

Parameters

location (str) – the location the response should redirect to.
code (int) – the redirect status code. defaults to 302.
Response (class) – a Response class to use when instantiating a response. The default is werkzeug.wrappers.Response if unspecified.

Return type

Response

werkzeug.utils.append_slash_redirect(environ, code=301)

Redirects to the same URL but with a slash appended. The behavior of this function is undefined if the path ends with a slash already.

Parameters

environ (WSGIEnvironment) – the WSGI environment for the request that triggers the redirect.
code (int) – the status code for the redirect.

Return type

Response

werkzeug.utils.send_file(path_or_file, environ, mimetype=None, as_attachment=False, download_name=None, conditional=True, etag=True, last_modified=None, max_age=None, use_x_sendfile=False, response_class=None, _root_path=None)

Send the contents of a file to the client.

The first argument can be a file path or a file-like object. Paths are preferred in most cases because Werkzeug can manage the file and get extra information from the path. Passing a file-like object requires that the file is opened in binary mode, and is mostly useful when building a file in memory with io.BytesIO.

Never pass file paths provided by a user. The path is assumed to be trusted, so a user could craft a path to access a file you didn’t intend.

If the WSGI server sets a file_wrapper in environ, it is used, otherwise Werkzeug’s built-in wrapper is used. Alternatively, if the HTTP server supports X-Sendfile, use_x_sendfile=True will tell the server to send the given path, which is much more efficient than reading it in Python.

Parameters

path_or_file (Union[os.PathLike, str, BinaryIO]) – The path to the file to send, relative to the current working directory if a relative path is given. Alternatively, a file-like object opened in binary mode. Make sure the file pointer is seeked to the start of the data.
environ (WSGIEnvironment) – The WSGI environ for the current request.
mimetype (Optional[str]) – The MIME type to send for the file. If not provided, it will try to detect it from the file name.
as_attachment (bool) – Indicate to a browser that it should offer to save the file instead of displaying it.
download_name (Optional[str]) – The default name browsers will use when saving the file. Defaults to the passed file name.
conditional (bool) – Enable conditional and range responses based on request headers. Requires passing a file path and environ.
etag (Union[bool, str]) – Calculate an ETag for the file, which requires passing a file path. Can also be a string to use instead.
last_modified (Optional[Union[datetime.datetime, int, float]]) – The last modified time to send for the file, in seconds. If not provided, it will try to detect it from the file path.
max_age (Optional[Union[int, Callable[[Optional[Union[os.PathLike, str]]], int]]]) – How long the client should cache the file, in seconds. If set, Cache-Control will be public, otherwise it will be no-cache to prefer conditional caching.
use_x_sendfile (bool) – Set the X-Sendfile header to let the server to efficiently send the file. Requires support from the HTTP server. Requires passing a file path.
response_class (Optional[Type[Response]]) – Build the response using this class. Defaults to Response.
_root_path (Optional[Union[os.PathLike, str]]) – Do not use. For internal use only. Use send_from_directory() to safely send files under a path.

Return type

Response

New in version 2.0: Adapted from Flask’s implementation.

Changed in version 2.0: download_name replaces Flask’s attachment_filename parameter. If as_attachment=False, it is passed with Content-Disposition: inline instead.

Changed in version 2.0: max_age replaces Flask’s cache_timeout parameter. conditional is enabled and max_age is not set by default.

Changed in version 2.0: etag replaces Flask’s add_etags parameter. It can be a string to use instead of generating one.

Changed in version 2.0: If an encoding is returned when guessing mimetype from download_name, set the Content-Encoding header.

werkzeug.utils.import_string(import_name, silent=False)

Imports an object based on a string. This is useful if you want to use import paths as endpoints or something similar. An import path can be specified either in dotted notation (xml.sax.saxutils.escape) or with a colon as object delimiter (xml.sax.saxutils:escape).

If silent is True the return value will be None if the import fails.

Parameters

import_name (str) – the dotted name for the object to import.
silent (bool) – if set to True import errors are ignored and None is returned instead.

Returns

imported object

Return type

Any

werkzeug.utils.find_modules(import_path, include_packages=False, recursive=False)

Finds all the modules below a package. This can be useful to automatically import all views / controllers so that their metaclasses / function decorators have a chance to register themselves on the application.

Packages are not returned unless include_packages is True. This can also recursively list modules but in that case it will import all the packages to get the correct load path of that module.

Parameters

import_path (str) – the dotted name for the package to find child modules.
include_packages (bool) – set to True if packages should be returned, too.
recursive (bool) – set to True if recursion should happen.

Returns

generator

Return type

Iterator[str]

werkzeug.utils.validate_arguments(func, args, kwargs, drop_extra=True)

Checks if the function accepts the arguments and keyword arguments. Returns a new (args, kwargs) tuple that can safely be passed to the function without causing a TypeError because the function signature is incompatible. If drop_extra is set to True (which is the default) any extra positional or keyword arguments are dropped automatically.

The exception raised provides three attributes:

missing: A set of argument names that the function expected but where missing.
extra: A dict of keyword arguments that the function can not handle but where provided.
extra_positional: A list of values that where given by positional argument but the function cannot accept.

This can be useful for decorators that forward user submitted data to a view function:

from werkzeug.utils import ArgumentValidationError, validate_arguments

def sanitize(f):
    def proxy(request):
        data = request.values.to_dict()
        try:
            args, kwargs = validate_arguments(f, (request,), data)
        except ArgumentValidationError:
            raise BadRequest('The browser failed to transmit all '
                             'the data expected.')
        return f(*args, **kwargs)
    return proxy

Parameters

func – the function the validation is performed against.
args – a tuple of positional arguments.
kwargs – a dict of keyword arguments.
drop_extra – set to False if you don’t want extra arguments to be silently dropped.

Returns

tuple in the form (args, kwargs).

Deprecated since version 2.0: Will be removed in Werkzeug 2.1. Use inspect.signature() instead.

werkzeug.utils.secure_filename(filename)

Pass it a filename and it will return a secure version of it. This filename can then safely be stored on a regular file system and passed to os.path.join(). The filename returned is an ASCII only string for maximum portability.

On windows systems the function also makes sure that the file is not named after one of the special device files.

>>> secure_filename("My cool movie.mov")
'My_cool_movie.mov'
>>> secure_filename("../../../etc/passwd")
'etc_passwd'
>>> secure_filename('i contain cool \xfcml\xe4uts.txt')
'i_contain_cool_umlauts.txt'

The function might return an empty filename. It’s your responsibility to ensure that the filename is unique and that you abort or generate a random filename if the function returned an empty one.

Changelog

New in version 0.5.

Parameters: filename (str) – the filename to secure
Return type: str

werkzeug.utils.bind_arguments(func, args, kwargs)

Bind the arguments provided into a dict. When passed a function, a tuple of arguments and a dict of keyword arguments bind_arguments returns a dict of names as the function would see it. This can be useful to implement a cache decorator that uses the function arguments to build the cache key based on the values of the arguments.

Parameters

func – the function the arguments should be bound for.
args – tuple of positional arguments.
kwargs – a dict of keyword arguments.

Returns

a dict of bound keyword arguments.

Deprecated since version 2.0: Will be removed in Werkzeug 2.1. Use Signature.bind() instead.

URL Helpers

Please refer to URL Helpers.

User Agent API

class werkzeug.user_agent.UserAgent(string)

Represents a parsed user agent header value.

The default implementation does no parsing, only the string attribute is set. A subclass may parse the string to set the common attributes or expose other information. Set werkzeug.wrappers.Request.user_agent_class to use a subclass.

Parameters: string (str) – The header value to parse.
Return type: None

New in version 2.0: This replaces the previous useragents module, but does not provide a built-in parser.

platform: Optional[str] = None: The OS name, if it could be parsed from the string.

browser: Optional[str] = None: The browser name, if it could be parsed from the string.

version: Optional[str] = None: The browser version, if it could be parsed from the string.

language: Optional[str] = None: The browser language, if it could be parsed from the string.

string: str: The original header value.

to_header()

Convert to a header value.

Return type: str

UserAgent Parsing (deprecated)

Deprecated since version 2.0: This module will be removed in Werkzeug 2.1. Subclass werkzeug.user_agent.UserAgent to use a dedicated parser instead.

class werkzeug.useragents.UserAgent(environ_or_string)

Represents a parsed user agent header value.

This uses a basic parser to try to extract some information from the header.

Parameters: environ_or_string (t.Union[str, WSGIEnvironment]) – The header value to parse, or a WSGI environ containing the header.
Return type: None

Deprecated since version 2.0: Will be removed in Werkzeug 2.1. Subclass werkzeug.user_agent.UserAgent (note the new module name) to use a dedicated parser instead.

Changed in version 2.0: Passing a WSGI environ is deprecated and will be removed in 2.1.

to_header()

Convert to a header value.

Return type: str

Security Helpers

Changelog

New in version 0.6.1.

werkzeug.security.generate_password_hash(password, method='pbkdf2:sha256', salt_length=16)

Hash a password with the given method and salt with a string of the given length. The format of the string returned includes the method that was used so that check_password_hash() can check the hash.

The format for the hashed string looks like this:

method$salt$hash

This method can not generate unsalted passwords but it is possible to set param method=’plain’ in order to enforce plaintext passwords. If a salt is used, hmac is used internally to salt the password.

If PBKDF2 is wanted it can be enabled by setting the method to pbkdf2:method:iterations where iterations is optional:

pbkdf2:sha256:80000$salt$hash
pbkdf2:sha256$salt$hash

Parameters

password (str) – the password to hash.
method (str) – the hash method to use (one that hashlib supports). Can optionally be in the format pbkdf2:method:iterations to enable PBKDF2.
salt_length (int) – the length of the salt in letters.

Return type

str

werkzeug.security.check_password_hash(pwhash, password)

Check a password against a given salted and hashed password value. In order to support unsalted legacy passwords this method supports plain text passwords, md5 and sha1 hashes (both salted and unsalted).

Returns True if the password matched, False otherwise.

Parameters

pwhash (str) – a hashed string like returned by generate_password_hash().
password (str) – the plaintext password to compare against the hash.

Return type

bool

werkzeug.security.safe_str_cmp(a, b)

This function compares strings in somewhat constant time. This requires that the length of at least one string is known in advance.

Returns True if the two strings are equal, or False if they are not.

Deprecated since version 2.0: Will be removed in Werkzeug 2.1. Use hmac.compare_digest() instead.

Changelog

New in version 0.7.

Parameters

a (str) –
b (str) –

Return type

bool

werkzeug.security.safe_join(directory, *pathnames)

Safely join zero or more untrusted path components to a base directory to avoid escaping the base directory.

Parameters

directory (str) – The trusted base directory.
pathnames (str) – The untrusted path components relative to the base directory.

Returns

A safe path, otherwise None.

Return type

Optional[str]

werkzeug.security.pbkdf2_hex(data, salt, iterations=260000, keylen=None, hashfunc=None)

Like pbkdf2_bin(), but returns a hex-encoded string.

Parameters

data (Union[str, bytes]) – the data to derive.
salt (Union[str, bytes]) – the salt for the derivation.
iterations (int) – the number of iterations.
keylen (Optional[int]) – the length of the resulting key. If not provided, the digest size will be used.
hashfunc (Optional[Union[str, Callable]]) – the hash function to use. This can either be the string name of a known hash function, or a function from the hashlib module. Defaults to sha256.

Return type

str

Deprecated since version 2.0: Will be removed in Werkzeug 2.1. Use hashlib.pbkdf2_hmac() instead.

Changelog

New in version 0.9.

werkzeug.security.pbkdf2_bin(data, salt, iterations=260000, keylen=None, hashfunc=None)

Returns a binary digest for the PBKDF2 hash algorithm of data with the given salt. It iterates iterations times and produces a key of keylen bytes. By default, SHA-256 is used as hash function; a different hashlib hashfunc can be provided.

Parameters

data (Union[str, bytes]) – the data to derive.
salt (Union[str, bytes]) – the salt for the derivation.
iterations (int) – the number of iterations.
keylen (Optional[int]) – the length of the resulting key. If not provided the digest size will be used.
hashfunc (Optional[Union[str, Callable]]) – the hash function to use. This can either be the string name of a known hash function or a function from the hashlib module. Defaults to sha256.

Return type

bytes

Deprecated since version 2.0: Will be removed in Werkzeug 2.1. Use hashlib.pbkdf2_hmac() instead.

Changelog

New in version 0.9.

Logging

Werkzeug uses standard Python logging. The logger is named "werkzeug".

import logging
logger = logging.getLogger("werkzeug")

If the logger level is not set, it will be set to INFO on first use. If there is no handler for that level, a StreamHandler is added.