fix test for python 3.7

Author: wonkajin

Diff for: docker-compose-test.yml

@@ -51,4 +51,4 @@ services:
       - percona-5.7
 
 networks:
-  default: {}
+  default: {}

Diff for: pymysqlreplication/tests/test_basic.py

@@ -770,8 +770,8 @@ def setUp(self):
         ctl_db = copy.copy(self.database)
         ctl_db["db"] = None
         ctl_db["port"] = 3307
-        if ctl_host := os.environ.get("MYSQL_5_7_CTL"):
-            ctl_db["host"] = ctl_host
+        if os.environ.get("MYSQL_5_7_CTL") is not None:
+            ctl_db["host"] = os.environ.get("MYSQL_5_7_CTL")
         self.ctl_conn_control = pymysql.connect(**ctl_db)
         self.ctl_conn_control.cursor().execute("DROP DATABASE IF EXISTS pymysqlreplication_test")
         self.ctl_conn_control.cursor().execute("CREATE DATABASE pymysqlreplication_test")

Diff for: test.Dockerfile

@@ -13,4 +13,4 @@ ARG MYSQL_5_7
 ENV MYSQL_5_7 ${MYSQL_5_7}
 
 ARG MYSQL_5_7_CTL
-ENV MYSQL_5_7_CTL ${MYSQL_5_7_CTL}
+ENV MYSQL_5_7_CTL ${MYSQL_5_7_CTL}