Question

我正在尝试创建一个程序，该程序读取文件的各行，并取每一行的总和并进行打印。它应该跳过仅是注释且为空的行，但在对行进行计数时仍要对其进行计数。该程序还应该能够从文件中创建变量并使用它们。我目前编写了以下代码：

import sys

class BadStatement(Exception):
    #creates an exeption called BadStatement to be used in exception handling
    pass


def interpret_statements(filename):
    #opens a file, checks if it is a valid file, and runs the program
    try:
        with open(filename) as f:
            lines = f.readlines()
    except FileNotFoundError:
        print('specify filename')
    loop_lines(lines)

def loop_lines(lines):
    #goes through each line in the file prints the sums
    line_num=1
    line_sum=0
    for line in lines:
        line_sum=process_line(line)
        line_num=line_num+1
        if line_sum == None:
            print("Line %i: Invalid Statement" %(line_num))
        elif line_sum==0:
            continue
        else:
            print("Line %i: %s" %(line_num, line_sum))

def process_line(line):
    #takes each line in the file and preforms the calculations in order to get the value of each line
    num_list=line.split()
    variable_dict = {}
    add = True
    line_sum = 0
    try:
        for token in num_list:
            if token in "abcdefghijklmnopqrstuvwxyz":
                check_variable(variable_dict, token)
            elif token == '+':
                add = True
            elif token == '-':
                add = False
            elif token == '':
                continue
            else:
                raise BadStatement
            try:
                if add == True:
                    line_sum += float(token)
                elif add== False:
                    line_sum -= float(token)
            except ValueError:
                raise BadStatement
        return line_sum
    except BadStatement:
        return None

def check_variable(variable_dict, line):
    #checks to make sure all noninteger values are defined
    num_list1 = line.split()
    sum=0
    for each in num_list1:
        if num_list1[0] == "=":
            sum=num_list1[2]
            if num_list1[each.index-1] == '+':
                sum += float(each)
            elif num_list1[each.index-1] =='-':
                sum -=float(each)
        return sum
    variable_dict[num_list1[0]] = sum
    return variable_dict

def check_for_valid_number(line):
    number_valid = False
    while number_valid == False:
        try:
            process_line(line) 
            number_valid = True
        except ValueError:
            pass

文件示例如下：

# Test correct expression statements
14.4
    23.4 + -19 +   98223
10 - 34 + 12.66 - 28 - 3323.2 + 12
14.3 
92 - 13   # here is a comment after an expression
     34 + 13#and another comment

# Test correct assignment statements
x123 = 19278
    salary = 873 - 13 
time = -123.33 + salary - 123 + 23 + 0 + -123 - x123
x123 = x123 + 15  # reassign the value of x123

# And expression statements with variables
  x123
  14.4 - salary
  time + salary - 10 + x123

# Now test some invalid statements
1474 +
820.34 - junk  # junk has not been defined
2884 - -1293 + 399 t 266
23.8 - 203.3 +
+     123.2 - 23.2
2884.2 + 293 - 23.2 283.3 + +
34.8 273 - 12
x =
x = salary + time = 15
x$y34 = 17 
19 = 19   
1xyz = 123

示例文件中的空格和古怪的格式是有意的。当前，所有行都作为无效语句返回。任何帮助将不胜感激。

Answer 1

该程序很难修复，有很多错误（实际上，我认为很难找到正确的方法）。举个例子，考虑文件的第一行非注释行：

x123 = 19278

该代码将无法解析它：num_list1将是：

["x123", "=", "19278"]

第if个案例都不适用于第一个项目，其中token为"x123"。

token in "abcdefghijklmnopqrstuvwxyz"是错误的
token == '+'是错误的
token == '-'是错误的
token == ''是错误的

所以我们进入raise BadStatement

无法在文件python中返回行的总和或差

1 个答案: