75 lines
2.5 KiB
Python
75 lines
2.5 KiB
Python
import token
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def get_tokens_from_expression_string(expression_string):
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"""
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Takes user input of an actuarial formula and parses the formula to id its components.
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:return: tokens (List of objects of CToken class).
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"""
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tokens = [] # List of objects of CToken class
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tmp = ""
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parsing_number = False
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symbols_dic = {} # Dictionary to keep track of the no. of times each variable appears.
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for i in range(0, len(expression_string)):
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c = expression_string[i]
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if c == '.' or c.isdigit():
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if tmp.count('.') == 1:
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raise SyntaxError("Invalid grammar, to many periods in number. Found at position " + str (i) + ".")
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if len(tokens) > 1:
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lookBehind = tokens[-1]
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if lookBehind.type == token.TokenType.exp_end:
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tokens.append(token.CToken("^", token.TokenType.power))
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if (i + 1) == len(expression_string):
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tokens.append(token.CToken(tmp + c, token.TokenType.constant))
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parsing_number = True
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tmp = tmp + c
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continue
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elif c == '(':
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if parsing_number:
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tokens.append(token.CToken(tmp, token.TokenType.constant))
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tokens.append(token.CToken("*", token.TokenType.multiply))
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tokens.append(token.CToken("(", token.TokenType.exp_start))
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parsing_number = False
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tmp = ""
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continue
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elif c == ')':
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if parsing_number:
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tokens.append(token.CToken(tmp, token.TokenType.constant))
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tokens.append(token.CToken(")", token.TokenType.exp_end))
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parsing_number = False
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tmp = ""
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continue
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elif token.TokenType.get_operator(c) != token.TokenType.unknown:
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if parsing_number:
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tokens.append(token.CToken(tmp, token.TokenType.constant))
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tokens.append(token.CToken(c, token.TokenType.get_operator(c)))
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parsing_number = False
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tmp = ""
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continue
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elif c != ' ':
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if len(tokens) > 1:
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lookBehind = tokens[-1]
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if lookBehind.type == token.TokenType.exp_end:
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tokens.append(token.CToken("^", token.TokenType.power))
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if (i + 1) < len(expression_string):
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lookAHead = expression_string[i + 1]
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if lookAHead == '(':
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tokens.append(token.CToken(c, token.TokenType.variable))
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tokens.append(token.CToken("*", token.TokenType.multiply))
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tmp = ""
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parsing_number = False
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continue
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if parsing_number:
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tokens.append(token.CToken(tmp, token.TokenType.constant))
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tokens.append(token.CToken("*", token.TokenType.multiply))
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if c in symbols_dic.keys():
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symbols_dic[c] += 1
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else:
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symbols_dic[c] = 1
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tokens.append(token.CToken(c + str(symbols_dic[c]), token.TokenType.variable))
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parsing_number = False
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tmp = ""
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return tokens
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