我有一个
组成的grade.txt。Mickey,Mouse,90*
Jane,Doe,50
Minnie,Mouse,95
Donald,Duck,80
Daffy,Duck,70
在计算平均值时，尝试读取文件并拆分以分开名称和等级。我收到未定义的行。
def main ():
with open('grade.txt' , 'r') as f:
lines = f.readlines(); #reads all the line in file to lines list.
f.close(); #closes f stream.
sum = 0; #initialised sum to store the sum of all grades.
print('Name Grade');
print('--------------------');
for line in lines: #loops through the lines list
str = line.split(','); #splits each line based on ','
grade = int(str[2]); #converts string to numeric value.
sum += grade; #adds the grade value to sum.
print(str[0]," ",str[1]," ",grade); #prints the line read after splitting.
print('Average Grade: ',round((sum/len(lines)),1)); #prints average of all grades by rounding it to 1 place.
newdata = input('Enter firstname,lastname and grade: '); #prompts user.
with open('grade.txt', 'a') as f: #opens file in append mode.
f.write('\n'+newdata); #writes data into file in new line.
f.close(); #closes f stream
main ()
朝着正确方向的协助表示赞赏。
出现错误
Traceback (most recent call last):
File "main.py", line 13, in <module>
for line in lines: #loops through the lines list
NameError: name 'lines' is not defined
修改后的代码
def main ():
with open('grades.txt' , 'r') as f:
lines = f.readlines(); #reads all the line in file to lines list.
sum = 0; #initialised sum to store the sum of all grades.
print('Name Grade');
print('--------------------');
for line in lines: #loops through the lines list
str = line.split(','); #splits each line based on ','
grade = int(str[2]); #converts string to numeric value.
sum += grade; #adds the grade value to sum.
print(str[0]," ",str[1]," ",grade); #prints the line read after splitting.
print('Average Grade: ',round((sum/len(lines)),1)); #prints average of all grades by rounding it to 1 place.
newdata = input('Enter firstname,lastname and grade: '); #prompts user.
with open('grades.txt', 'a') as f: #opens file in append mode.
f.write('\n'+newdata); #writes data into file in new line.
f.close(); #closes f stream
谢谢，我通过缩进传递了行错误，并删除了f.close;。通过，我看到我的代码没有输出文件的内容。这只是打印newdata
答案 0 :(得分：1)
创建lines之类的变量时，只能在创建它的函数中使用它。
您的主函数实际上在行f.close();之后结束。为了使一切成为您的主要功能的一部分，您需要保持相同的缩进级别。
def main ():
with open('grade.txt' , 'r') as f:
lines = f.readlines(); #reads all the line in file to lines list.
f.close(); #closes f stream.
sum = 0; #initialised sum to store the sum of all grades.
print('Name Grade');
print('--------------------');
for line in lines: #loops through the lines list
str = line.split(','); #splits each line based on ','
grade = int(str[2]); #converts string to numeric value.
sum += grade; #adds the grade value to sum.
print(str[0]," ",str[1]," ",grade); #prints the line read after splitting.
print('Average Grade: ',round((sum/len(lines)),1)); #prints average of all grades by rounding it to 1 place.
newdata = input('Enter firstname,lastname and grade: '); #prompts user.
with open('grade.txt', 'a') as f: #opens file in append mode.
f.write('\n'+newdata); #writes data into file in new line.
f.close(); #closes f stream
main ()
与您的代码有关的几个指针。在Python中，每行的末尾不需要分号。
使用f.close()块时，不需要行with。该文件在with块的结尾处自动关闭。
答案 1 :(得分：0)
它与可变范围有关。
with open('grade.txt', 'r') as f:
lines = f.readlines()
行是在with语句内定义的，因此在with语句退出（文件关闭）时不再存在。
根据您的缩进以及因此可变的范围，在“使用”行的位置很重要。
with open('grade.txt', 'r') as f:
lines = f.readlines()
# "lines" is visible here.
do_something_here()
# "lines" is not defined here.
for line in lines:
wont_work()
但是，如果在with语句之外定义行，则代码将起作用。这可以改变“行”的范围，并使其在整个with语句中持续存在，尽管这可以说是更松散的代码。例如：
lines = []
with open('grade.txt', 'r') as f:
lines = f.readlines()
# lines persists and now contains the content of the file. So you can still operate on it.
do_something_here()
简单的解决方案：
def main():
print("Name Grade")
print('-------------------------')
with open('grade.txt', 'r') as file:
sum = 0
count = 0
for line in file:
# Strip the line of all white space and new lines "\n" usually found in text files.
# Also strip the "*" found in the original input file.
# Split content based on ",".
entry = line.strip().strip("*").split(',')
# Extract name and grade.
name = entry[0] + " " + entry[1]
grade = entry[2]
print("{:<20}{:>2}".format(name, grade))
sum += int(grade)
count += 1
print("Average Grade: {:.1f}".format(sum / count))
if __name__ == '__main__':
main()
有关Python的说明：
with open('grade.txt', 'r') as file:
for line in file:
# efficient memory usage
do_something
print(type(file))
输出：
<class '_io.TextIOWrapper'>