Tests: switched to using f-strings.

Previously, it was necessary to support older versions of Python for
compatibility.  F-strings were released in Python 3.6.  Python 3.5 was
marked as unsupported by the end of 2020, so now it's possible to start
using f-strings safely for better readability and performance.

test/python/environment/wsgi.py

@@ -2,13 +2,10 @@ import os
 
 
 def application(env, start_response):
-    body = ''
     vars = env.get('HTTP_X_VARIABLES').split(',')
 
-    for var in vars:
-        if var in os.environ:
-            body += str(os.environ[var]) + ','
-
+    body = ','.join([str(os.environ[var]) for var in vars if var in os.environ])
     body = body.encode()
+
     start_response('200', [('Content-Length', str(len(body)))])
     return body

test/python/input_readline_size/wsgi.py

@@ -9,7 +9,7 @@ def application(environ, start_response):
         body.append(l)
 
         if len(l) > 9:
-            body.append(b'len(l) > 9: ' + l)
+            body.append(f'len(l) > 9: {l}'.encode())
             break
 
     start_response('200', [('X-Lines-Count', str(len(body)))])

test/python/lifespan/empty/asgi.py

@@ -3,17 +3,17 @@ import os
 
 async def handler(prefix, scope, receive, send):
     if scope['type'] == 'lifespan':
-        with open(prefix + 'version', 'w+') as f:
+        with open(f'{prefix}version', 'w+') as f:
             f.write(
-                scope['asgi']['version'] + ' ' + scope['asgi']['spec_version']
+                f"{scope['asgi']['version']} {scope['asgi']['spec_version']}"
             )
         while True:
             message = await receive()
             if message['type'] == 'lifespan.startup':
-                os.remove(prefix + 'startup')
+                os.remove(f'{prefix}startup')
                 await send({'type': 'lifespan.startup.complete'})
             elif message['type'] == 'lifespan.shutdown':
-                os.remove(prefix + 'shutdown')
+                os.remove(f'{prefix}shutdown')
                 await send({'type': 'lifespan.shutdown.complete'})
                 return
 
@@ -22,7 +22,9 @@ async def handler(prefix, scope, receive, send):
             {
                 'type': 'http.response.start',
                 'status': 204,
-                'headers': [(b'content-length', b'0'),],
+                'headers': [
+                    (b'content-length', b'0'),
+                ],
             }
         )
 

test/python/targets/wsgi.py

@@ -9,9 +9,6 @@ def wsgi_target_b(env, start_response):
 
 
 def wsgi_target_prefix(env, start_response):
-    data = u'%s %s' % (
-        env.get('SCRIPT_NAME', 'No Script Name'),
-        env['PATH_INFO'],
-    )
-    start_response('200', [('Content-Length', '%d' % len(data))])
+    data = f"{env.get('SCRIPT_NAME', 'No Script Name')} {env['PATH_INFO']}"
+    start_response('200', [('Content-Length', f'{data}')])
     return [data.encode('utf-8')]

test/python/threading/asgi.py

@@ -11,9 +11,7 @@ class Foo(threading.Thread):
         threading.Thread.__init__(self)
 
     def log_index(self, index):
-        sys.stderr.write(
-            "(" + str(index) + ") Thread: " + str(self.__x) + "\n"
-        )
+        sys.stderr.write(f'({index}) Thread: {self.__x}\n')
         sys.stderr.flush()
 
     def run(self):

test/python/threading/wsgi.py

@@ -11,9 +11,7 @@ class Foo(threading.Thread):
         threading.Thread.__init__(self)
 
     def log_index(self, index):
-        sys.stderr.write(
-            "(" + str(index) + ") Thread: " + str(self.__x) + "\n"
-        )
+        sys.stderr.write(f'({index}) Thread: {self.__x}\n')
         sys.stderr.flush()
 
     def run(self):

test/python/unicode/wsgi.py

@@ -1,7 +1,7 @@
 def application(environ, start_response):
     temp_dir = environ.get('HTTP_TEMP_DIR')
 
-    with open(temp_dir + '/tempfile', 'w') as f:
+    with open(f'{temp_dir}/tempfile', 'w') as f:
         f.write('\u26a0\ufe0f')
 
     start_response('200', [('Content-Length', '0')])