The module-level attributes added in d64b291 to set global defaults were not working

This fixes the problem and restores the documentation that was previously reverted in b87f8d3.

Author: JoshData

README.md

@@ -139,16 +139,16 @@ The `validate_email` function also accepts the following keyword arguments
 
 `allow_smtputf8=True`: Set to `False` to prohibit internationalized addresses that would
     require the
-    [SMTPUTF8](https://tools.ietf.org/html/rfc6531) extension.
+    [SMTPUTF8](https://tools.ietf.org/html/rfc6531) extension. You can also set `email_validator.ALLOW_SMTPUTF8` to `False` to turn it off for all calls by default.
 
-`check_deliverability=True`: Set to `False` to skip the domain name DNS record checks.
+`check_deliverability=True`: Set to `False` to skip the domain name DNS record checks. You can also set `email_validator.CHECK_DELIVERABILITY` to `False` to turn it off for all calls by default.
 
 `allow_empty_local=False`: Set to `True` to allow an empty local part (i.e.
     `@example.com`), e.g. for validating Postfix aliases.
 
 `dns_resolver=None`: Pass an instance of [dns.resolver.Resolver](https://dnspython.readthedocs.io/en/latest/resolver-class.html) to control the DNS resolver including setting a timeout and [a cache](https://dnspython.readthedocs.io/en/latest/resolver-caching.html). The `caching_resolver` function shown above is a helper function to construct a dns.resolver.Resolver with a [LRUCache](https://dnspython.readthedocs.io/en/latest/resolver-caching.html#dns.resolver.LRUCache). Reuse the same resolver instance across calls to `validate_email` to make use of the cache.
 
-`test_environment=False`: DNS-based deliverability checks are disabled and  `test` and `subdomain.test` domain names are permitted (see below).
+`test_environment=False`: DNS-based deliverability checks are disabled and  `test` and `subdomain.test` domain names are permitted (see below). You can also set `email_validator.TEST_ENVIRONMENT` to `True` to turn it on for all calls by default.
 
 ### DNS timeout and cache
 
@@ -165,10 +165,11 @@ while True:
 
 ### Test addresses
 
-This library rejects email addresess that use the [Special Use Domain Names](https://www.iana.org/assignments/special-use-domain-names/special-use-domain-names.xhtml) `invalid`, `localhost`, `test`, and some others by raising `EmailUndeliverableError`. This is to protect your system from abuse: You probably don't want a user to be able to cause an email to be sent to `localhost`. However, in your non-production test environments you may want to use `@test` or `@myname.test` email addresses. There are two ways you can allow this:
+This library rejects email addresess that use the [Special Use Domain Names](https://www.iana.org/assignments/special-use-domain-names/special-use-domain-names.xhtml) `invalid`, `localhost`, `test`, and some others by raising `EmailUndeliverableError`. This is to protect your system from abuse: You probably don't want a user to be able to cause an email to be sent to `localhost`. However, in your non-production test environments you may want to use `@test` or `@myname.test` email addresses. There are three ways you can allow this:
 
-A. Add `test_environment=True` to the call to `validate_email` (see above).
-B. Remove the special-use domain name that you want to use from `email_validator.SPECIAL_USE_DOMAIN_NAMES`:
+1. Add `test_environment=True` to the call to `validate_email` (see above).
+2. Set `email_validator.TEST_ENVIRONMENT` to `True`.
+3. Remove the special-use domain name that you want to use from `email_validator.SPECIAL_USE_DOMAIN_NAMES`:
 
 ```python
 import email_validator

email_validator/__init__.py

@@ -251,7 +251,9 @@ def __get_length_reason(addr, utf8=False, limit=EMAIL_MAX_LENGTH):
     return reason.format(prefix, diff, suffix)
 
 
-def caching_resolver(timeout=DEFAULT_TIMEOUT, cache=None):
+def caching_resolver(timeout=None, cache=None):
+    if timeout is None:
+        timeout = DEFAULT_TIMEOUT
     resolver = dns.resolver.Resolver()
     resolver.cache = cache or dns.resolver.LRUCache()
     resolver.lifetime = timeout  # timeout, in seconds
@@ -260,11 +262,11 @@ def caching_resolver(timeout=DEFAULT_TIMEOUT, cache=None):
 
 def validate_email(
     email,
-    allow_smtputf8=ALLOW_SMTPUTF8,
+    allow_smtputf8=None,
     allow_empty_local=False,
-    check_deliverability=CHECK_DELIVERABILITY,
-    test_environment=TEST_ENVIRONMENT,
-    timeout=DEFAULT_TIMEOUT,
+    check_deliverability=None,
+    test_environment=None,
+    timeout=None,
     dns_resolver=None
 ):
     """
@@ -273,6 +275,16 @@ def validate_email(
     but if bytes it must be ASCII-only.
     """
 
+    # Fill in default values of arguments.
+    if allow_smtputf8 is None:
+        allow_smtputf8 = ALLOW_SMTPUTF8
+    if check_deliverability is None:
+        check_deliverability = CHECK_DELIVERABILITY
+    if test_environment is None:
+        test_environment = TEST_ENVIRONMENT
+    if timeout is None:
+        timeout = DEFAULT_TIMEOUT
+
     # Allow email to be a str or bytes instance. If bytes,
     # it must be ASCII because that's how the bytes work
     # on the wire with SMTP.
@@ -579,6 +591,8 @@ def validate_email_domain_part(domain, test_environment=False):
 def validate_email_deliverability(domain, domain_i18n, timeout=DEFAULT_TIMEOUT, dns_resolver=None):
     # Check that the domain resolves to an MX record. If there is no MX record,
     # try an A or AAAA record which is a deprecated fallback for deliverability.
+    # (Note that changing the DEFAULT_TIMEOUT module-level attribute
+    #  will not change the default value of this method's timeout argument.)
 
     # If no dns.resolver.Resolver was given, get dnspython's default resolver.
     # Override the default resolver's timeout. This may affect other uses of