137 lines
4.6 KiB
Python
137 lines
4.6 KiB
Python
from base_unit import Token, TokenType
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from collections import deque
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def get_tokens_from_expression_string(expression_string):
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# Takes user input (in the format of a string) of an actuarial formula and parses the formula to its components.
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# Returns the list of Token objects that represent the string expression.
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tokens = deque()
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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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variable_is_negative = False
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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 c == '.' and 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 == TokenType.exp_end:
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tokens.append(token.Token("^", TokenType.power))
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if (i + 1) == len(expression_string):
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tokens.append(token.Token(tmp + c, 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 == '-' and not parsing_number:
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if expression_string[i + 1] == '.' or expression_string[i + 1].isdigit():
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if token.TokenType.get_operator(tokens[-1].value) != TokenType.unknown:#tokens[-1].type == token.TokenType
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#print(tokens[-1].value)
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#tokens.append(token.Token('+', token.TokenType.add))
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parsing_number = True
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tmp = "-"
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elif tokens[-1].type == TokenType.exp_start:
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parsing_number = True
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tmp = "-"
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elif tokens[-1].type == TokenType.exp_end:
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tokens.append(Token(c, TokenType.get_operator(c)))
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parsing_number = False
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tmp = ""
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elif expression_string[i + 1].isalpha():
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# Must be a variable.
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if tokens[-1].type == TokenType.exp_start:
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variable_is_negative = True
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elif token.TokenType.get_operator(tokens[-1].value) != TokenType.unknown:
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variable_is_negative = True
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elif tokens[-1].type == TokenType.exp_end:
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tokens.append(Token(c, TokenType.get_operator(c)))
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parsing_number = False
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tmp = ""
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else:
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tokens.append(Token(c, TokenType.get_operator(c)))
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parsing_number = False
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tmp = ""
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elif c == '(':
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if parsing_number:
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tokens.append(token.Token(tmp, TokenType.constant))
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tokens.append(token.Token("*", TokenType.multiply))
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tokens.append(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.Token(tmp, TokenType.constant))
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tokens.append(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 TokenType.get_operator(c) != TokenType.unknown:
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if parsing_number:
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tokens.append(Token(tmp, TokenType.constant))
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tokens.append(Token(c, 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 == TokenType.exp_end:
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tokens.append(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(c, TokenType.variable))
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tokens.append(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(tmp, TokenType.constant))
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tokens.append(Token("*", TokenType.multiply))
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# Check to see if the encountered variable, which is effectively a single character,
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# has been seen before. If it has been then simply increment the number that represents how many times it's been seen
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# else, add a new entry for it in the dictonary 'symbols_dic'.
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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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# Afterwards, add the variable with the count of the times it's been seen as a token object to the list of tokens.
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tokens.append(Token(c + str(symbols_dic[c]), TokenType.variable, variable_is_negative))
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variable_is_negative = False
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parsing_number = False
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tmp = ""
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return tokens
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def peek_list(tokens):
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# Returns the last Token object in the list, else throws an error.
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if tokens:
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return tokens[-1]
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else:
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raise IndexError("The token list is empty.", tokens)
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def print_token_list(tokens):
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# Prints the list of Tokens to standard out.
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for tk in tokens:
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if tk.type == TokenType.variable:
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if tk.is_negative_variable:
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print("-%s " %(tk.value), end = "")
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else:
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print("%s " %(tk.value), end ="")
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else:
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print("%s " %(tk.value), end = "")
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print()
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def stringify_token_list(tokens):
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# Returns a string that represents the list of Tokens.
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text = ''
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for tk in tokens:
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text += str(tk.value)
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return text
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