从 mongodb 到 python 的字符串作为原始字符串已解决但 parse_latex 的新问题

Question

i am getting following as string from MongoDB query:

1000*\frac{1-{(\frac{1}{1+0.1025})^{10}}}{0.09806}'

like to take it to equate to expression

expression = '1000*\frac{1-{(\frac{1}{1+0.1025})^{10}}}{0.09806}'

then convert to sympy expression with

expression_fin = parse_latex(expression)

but I got errors as this is not a raw string

I tried the following:

expression1=f'{expression}'
expression = repr('1000*\frac{1-{(\frac{1}{1+0.1025})^{10}}}{0.09806}')

both attempts does not works please help if any Edited:

    def step_exec(step_id, part_req):
    print('printing here')
    newEq=repr(part_req['extras'][0]['fn_e8wgwASbHjuLR7Mb6mH2pC'])
    print(newEq)
    # rawtest = r'%s' % newEq

    rawtest = parse_expr(newEq, evaluate=False)
    sympy_inputFrom_parse_expr=parse_latex(rawtest)
    print('sympy_inputFrom_parse_expr',sympy_inputFrom_parse_expr)
    latex_inputFromSympy=latex(sympy_inputFrom_parse_expr)
    print('latex_inputFromSympy',latex_inputFromSympy)
    print(latex_inputFromSympy == part_req['extras'][0]['fn_e8wgwASbHjuLR7Mb6mH2pC'])

    pprint.pprint(part_req['extras'][0]['fn_e8wgwASbHjuLR7Mb6mH2pC'])

    print('raw here')
    rawRstring=r'1200*\frac{1-{(\frac{1}{1+0.1259})^{12}}}{0.11917}'
    print('rawRstring',rawRstring)
    parsLatToSympy = parse_latex(rawRstring)
    print('parsLatToSympy',parsLatToSympy)
    SympyTOlatex=latex(parsLatToSympy)
    print('SympyTOlatex',SympyTOlatex)
    print('latex_inputFromSympy', latex_inputFromSympy)

    return step_id

the result:

printing here

'1200*\frac{1-{(\frac{1}{1+0.1259})^{12}}}{0.11917}'

sympy_inputFrom_parse_expr 1200*((1 - 1/(0.1259 + 1)**12)/0.11917)

latex_inputFromSympy 1200 \frac{1 - \frac{1}{\left(0.1259 + 1\right)^{12}}}{0.11917}

False

'1200*\frac{1-{(\frac{1}{1+0.1259})^{12}}}{0.11917}'

raw here

rawRstring 1200*\frac{1-{(\frac{1}{1+0.1259})^{12}}}{0.11917}

parsLatToSympy 1200*((1 - 1/(0.1259 + 1)**12)/0.11917)

SympyTOlatex 1200 \frac{1 - \frac{1}{\left(0.1259 + 1\right)^{12}}}{0.11917}

latex_inputFromSympy 1200 \frac{1 - \frac{1}{\left(0.1259 + 1\right)^{12}}}{0.11917}

the raw string problem is solved from "parse_expr" but it changes the expression please help if any

Answer 1

Raw string can be created by prefixing a string literal with r"" . In your case:

from sympy.parsing.latex import parse_latex
r_string = r"1000*\frac{1-{(\frac{1}{1+0.1025})^{10}}}{0.09806}"
expression = parse_latex(r_string)
expression

EDIT to accommodate comment. Yeah, nice problem you have :) For your specific case you cold do this s.encode('unicode_escape').decode() . But this is likely going to modify the characters following backslashes, so you would also have to perform a replacement to bring them back to the original intent. For example:

s = "1000*\frac{1-{(\frac{1}{1+0.1025})^{10}}}{0.09806}"
# convert to raw, according to https://stackoverflow.com/a/65380295/2329968
r_string = s.encode('unicode_escape').decode()
# at this point you have a problem: the character inside s following a
# backslash might change to something else. Need to bring it back
r_string_mod = r_string.replace("x0c", "f")
parse_latex(r_string_mod)