修复了部分文档和代码中的bug

Day01-15/Day04/code/for1.py

@@ -8,6 +8,5 @@ Date: 2018-03-01
 
 sum = 0
 for x in range(1, 101):
-    if x % 2 == 0:
     sum += x
 print(sum)

Day16-20/Python语言进阶.md

@@ -555,6 +555,7 @@
 
      ```Python
      from functools import wraps
+     from threading import Lock
      
      
      def singleton(cls):

Day36-40/code/SRS_create_and_init.sql

@@ -216,7 +216,7 @@ select stuname as 姓名, year(now())-year(stubirth) as 年龄 from tb_student w
 );
 
 -- 查询选了两门以上的课程的学生姓名(子查询/分组条件/集合运算)
-select stuname from tb_student where stuid=(
+select stuname from tb_student where stuid in (
 	select stuid from tb_score group by stuid having count(stuid)>2
 )
 

Day36-40/关系型数据库MySQL.md

@@ -401,7 +401,7 @@
    );
    
    -- 查询选了两门以上的课程的学生姓名(子查询/分组条件/集合运算)
-   select stuname from tb_student where stuid=(
+   select stuname from tb_student where stuid in (
    	select stuid from tb_score group by stuid having count(stuid)>2
    )