python这个代码如何声明全局变量filename

Question

def menu(): #创建一个开始菜单函数
print('=======================学生信息管理系统=======================')
print('---------------------------功能菜单--------------------------')
print('\t\t\t1.录入学生信息')
print('\t\t\t2.查找学生信息')
print('\t\t\t3.删除学生信息')
print('\t\t\t4.修改学生信息')
print('\t\t\t5.排序')
print('\t\t\t6.统计学生总人数')
print('\t\t\t7.显示所有学生信息')
print('\t\t\t0.退出')
def main():
while True:
menu()
choice = int(input('请选择：'))
if choice in [0, 1, 2, 3, 4, 5, 6, 7]:
if choice == 0:
answer = input('您确定要退出系统吗？y/n：')
if answer == 'y' or answer == 'Y':
print('谢谢您的使用！')
break
else:
continue
elif choice == 1:
insert()
elif choice == 2:
search()
elif choice == 3:
delete()
elif choice == 4:
modify()
elif choice == 5:
sort()
elif choice == 6:
total()
elif choice == 7:
show()
def insert():
student_list = []
while True:
id = input('请输入ID：')
if not id:
break
name = input('请输入学生姓名：')
if not name:
break

    try:
        subject1 = int(input('请输入科目1的成绩：'))
        subject2 = int(input('请输入科目2的成绩：'))
        subject3 = int(input('请输入科目3的成绩：'))
    except:
        print('输入无效，不是整数类型，请重新输入')
        continue
    #将录入的学生信息保存到字典
    student = {'id': id, 'name': name, 'subject1': subject1, 'subject2': subject2, 'subject3': subject3}
    #将学生信息添加到列表
    student_list.append(student)
    answer = input('是否继续添加？y/n：')
    if answer == 'y' or answer == 'Y':
        continue
    else:
        break
#调用save()函数
save(student_list)
print('学生信息录入完毕！')

def save(lst):
try:
stu_txt = open(filename, 'a', encoding='utf-8') #追加打开
except:
stu_txt = open(filename, 'w', encoding='utf-8') #写入打开
for item in lst:
stu_txt.write(str(item) + '\n') #遍历列表 转成字符串类型写入
stu_txt.close()
def search():
student_query = []
while True:
id = ''
name = ''
if os.path.exists(filename):
mode = input('按ID查找请输入1，按姓名查找请输入2：')
if mode == '1':
id = input('请输入学生ID：')
elif mode == '2':
name = input('请输入学生姓名：')
else:
print('您的输入有误，请重新输入')
search()
with open(filename, 'r', encoding='utf-8') as rfile:
student = rfile.readlines()
for item in student:
d = dict(eval(item))
if id != '':
if d['id'] == id:
student_query.append(d)
if name != '':
if d['name'] == name:
student_query.append(d)
#显示查询结果
show_student(student_query)
#清空列表
student_query.clear()
answer = input('是否要继续查询？y/n :')
if answer == 'y' or answer == 'Y':
continue
else:
break
def show_student(lst):
if len(lst) == 0:
print('没有查询到学生信息！！！')
return
#定义标题显示格式
format_title = '{:^6}\t{:^12}\t{:^8}\t{:^10}\t{:^10}\t{:^8}'
print(format_title.format('ID','姓名','科目1成绩','科目2成绩','科目3成绩','总成绩'))
#定义内容的显示格式
format_data = '{:^6}\t{:^13}\t{:^10}\t{:^12}\t{:^13}\t{:^12}'
for item in lst:
print(format_data.format(item.get('id'),
item.get('name'),
item.get('subject1'),
item.get('subject2'),
item.get('subject3'),
int(item.get('subject1')) + int(item.get('subject2')) + int(item.get('subject3'))
))
def delete():
while True:
student_id = input('请输入要删除的学生的ID：')
if student_id != '':
if os.path.exists(filename):
with open(filename, 'r', encoding='utf-8') as file:
student_old = file.readlines() #文件存在读取列表
else:
student_old = [] #不存在设为空
flag = False #标记是否删除
if student_old:
with open(filename, 'w', encoding='utf-8') as wfile:
d = {}
for item in student_old:
d = dict(eval(item)) #将字符串转成字典
if d['id'] != student_id:
wfile.write(str(d) + '\n')
else:
flag = True
if flag:
print(f'ID为{student_id}的学生信息已被删除')
else:
print(f'没有找到ID为{student_id}的学生信息')
else:
print('无该学生信息')
break
show() #删除后重新显示所有学生信息
answer = input('是否继续删除？y/n：')
if answer == 'y' or answer == 'Y':
continue
else:
break
def modify():
show()
if os.path.exists(filename):
with open(filename, 'r', encoding='utf-8') as rfile:
student_old = rfile.readlines()
else:
return
student_id = input('请输入要修改的学员的ID：')
if student_id != '':
with open(filename, 'w', encoding='utf-8') as wfile:
for item in student_old:
d = dict(eval(item))
if d['id'] == student_id:
print('找到该学生信息，可以修改他的相关信息了！')
try:
d['name'] = input('请输入姓名：')
d['subject1'] = input('请输入科目1的成绩：')
d['subject2'] = input('请输入科目2的成绩：')
d['subject3'] = input('请输入科目3的成绩：')
except:
print('您的输入有误，请重新输入！！！')
wfile.write(str(d) + '\n')
print('修改成功！')
else:
wfile.write(str(d) + '\n')
answer = input('是否继续修改其他学生的信息？y/n：')
if answer == 'y' or answer == 'Y':
modify()
def sort():
show()
if os.path.exists(filename):
with open(filename, 'r', encoding='utf-8') as rfile:
student_list = rfile.readlines()
student_new = []
for item in student_list:
d = dict(eval(item))
student_new.append(d)
else:
return
asc_or_desc = input('请选择（0.升序 1.降序）：')
if asc_or_desc == '0':
asc_or_desc_bool = False
elif asc_or_desc == '1':
asc_or_desc_bool = True
else:
print('您的输入有误，请重新输入')
sort()
mode = input('请选择排序方式（1.按科目1排序 2.按科目2排序 3.按科目3排序 0.按总成绩排序）:')
if mode == '1':
student_new.sort(key=lambda x: int(x['subject1']), reverse=asc_or_desc_bool)
elif mode == '2':
student_new.sort(key=lambda x: int(x['subject2']), reverse=asc_or_desc_bool)
elif mode == '3':
student_new.sort(key=lambda x: int(x['subject3']), reverse=asc_or_desc_bool)
elif mode == '0':
student_new.sort(key=lambda x: int(x['subject1'])+ int(x['subject2'])+ int(x['subject3']), reverse=asc_or_desc_bool)
else:
print('您的输入有误，请重新输入')
sort()
show_student(student_new)
def total():
if os.path.exists(filename):
with open(filename, 'r', encoding='utf-8') as rfile:
students = rfile.readlines()
if students:
print(f'一共有{len(students)}名学生')
else:
print('还未录入学生信息......')
else:
print('暂未保存数据信息......')
def show():
student_lst = []
if os.path.exists(filename):
with open(filename, 'r', encoding='utf-8') as rfile:
students = rfile.readlines()
for item in students:
student_lst.append(eval(item))
if student_lst:
show_student(student_lst)
else:
print('暂未保存过数据！！')

Answer 1

在文件的最开始处定义filename变量,在函数使用的时候,示例如下
定义

#文件第一行
filename='test.txt'

函数内使用方式

global filename#引入全局变量
open(filename, 'a', encoding='utf-8')#使用全局变量

如在你的save函数中调用全局变量filename

def save(lst):
    global filename
    try:
        stu_txt = open(filename, 'a', encoding='utf-8')  # 追加打开
    except:
        stu_txt = open(filename, 'w', encoding='utf-8')  # 写入打开
    for item in lst:
        stu_txt.write(str(item) + '\n')  # 遍历列表 转成字符串类型写入
    stu_txt.close()