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import re
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'''
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对给定的代数表达式字符串进行处理，包括格式化和转换，最终返回两个值：
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表达式中的参数列表
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经过转换后的表达式字符串
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'''
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def convert_log(expression):
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# 匹配log(x,b)的正则表达式
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pattern = r'log\((\w+),(\w+)\)'
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match = re.match(pattern, expression)
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if match:
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x = match.group(1)
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b = match.group(2)
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# 构造新表达式
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new_expression = f'(np.log({x}) + 1e-5) / (np.log({b}) + 1e-5)'
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return new_expression
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else:
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return None
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# 将表达式中的e^x转换为numpy库函数的形式np.exp(x)。
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def convert_e(expression):
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new_expression = 'np.exp'+expression[2:]
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return new_expression
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# 将三角函数（sin, cos, tan等）转换为使用numpy库函数的形式，例如sin(x)转换为np.sin(x)。
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def convert_trigonometric(expression):
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# 构造新表达式
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new_expression = 'np.'+expression
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return new_expression
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# 将指数形式x^y转换为numpy库函数的形式np.power(x, y)
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def convert_x(expression):
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# 匹配log(x,b)的正则表达式
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pattern = r'(\w+)\^(\w+)'
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match = re.match(pattern, expression)
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if match:
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base = match.group(1)
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exponent = match.group(2)
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# 构造新表达式
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new_expression = f'np.power({base}, {exponent})'
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return new_expression
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else:
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return None
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# 移除表达式括号内的空格
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def remove_inner_spaces(expression):
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# 匹配括号内的空格的正则表达式
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pattern = r'\((.*?)\)'
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# 替换匹配到的括号内的空格
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new_expression = re.sub(pattern, lambda match: '(' + match.group(1).replace(' ', '') + ')', expression)
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return new_expression
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# 在表达式中的运算符前后添加空格，以便后续操作。
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def add_spaces(expression):
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# 匹配运算符的正则表达式
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pattern = r'([+\-*/])'
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# 替换匹配到的运算符
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new_expression = re.sub(pattern, r' \1 ', expression)
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return new_expression
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# 查找表达式中x前面直接跟着字母但没有乘号*的位置，并修正
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def find_letter_index(string):
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pattern = r'([a-zA-Z])x\b'
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matches = re.findall(pattern, string)
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# print(matches)
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letter_indices = []
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for i in range(len(string)):
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if string[i] in matches:
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if string[i+1] == 'x':
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letter_indices.append(i)
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return letter_indices
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# 主要目的是处理一个代数表达式字符串，对其进行格式化和转换，然后返回两个值：一个是表达式中的参数列表，另一个是经过转换的表达式字符串。
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def expression_output(expression):
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# 示例使用
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modified_list = find_letter_index(expression) # 将x前没有*的加上
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index = 1
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for i in modified_list:
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expression = expression[0:index+i]+'*'+expression[index+i:]
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index += 1
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# print(expression)
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expression = add_spaces(expression)
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new_expression = remove_inner_spaces(expression)
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list_expression = new_expression.split(' ')
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conforms = ['e^', 'log', 'sin', 'cos', 'tan', '^']
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new_list = []
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for expres in list_expression:
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new_list.append(expres)
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for i in range(6):
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if conforms[i] in expres:
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index = list_expression.index(expres)
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if i == 0:
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list_expression[index] = convert_e(expres)
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elif i == 1:
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list_expression[index] = convert_log(expres)
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elif i == 5:
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list_expression[index] = convert_x(expres)
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else:
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list_expression[index] = convert_trigonometric(expres)
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new_list[-1] = new_list[-1].replace(conforms[i], "")
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break
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new_list = [char for item in new_list for char in item if char.isalpha()]
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parameter = 'x,'
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for item in new_list:
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if item not in parameter and item != 'x':
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parameter = parameter+item+','
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for item in new_list:
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if item not in parameter:
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parameter = parameter+item+','
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str_expression = ''
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for item in list_expression:
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str_expression = str_expression + item
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if len(parameter[:-1]) > 1:
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return parameter[:-1], str_expression
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else:
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return None, None
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