mirror of https://github.com/python/cpython
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Guido van Rossum
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# General floating point formatting functions.
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# Functions:
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# fix(x, digits_behind)
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# sci(x, digits_behind)
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# Each takes a number or a string and a number of digits as arguments.
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# Parameters:
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# x: number to be formatted; or a string resembling a number
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# digits_behind: number of digits behind the decimal point
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import regex
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# Compiled regular expression to "decode" a number
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decoder = regex.compile( \
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'^\([-+]?\)0*\([0-9]*\)\(\(\.[0-9]*\)?\)\(\([eE][-+]?[0-9]+\)?\)$')
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# \0 the whole thing
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# \1 leading sign or empty
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# \2 digits left of decimal point
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# \3 fraction (empty or begins with point)
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# \5 exponent part (empty or begins with 'e' or 'E')
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NotANumber = 'fpformat.NotANumber'
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# Return (sign, intpart, fraction, expo) or raise an exception:
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# sign is '+' or '-'
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# intpart is 0 or more digits beginning with a nonzero
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# fraction is 0 or more digits
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# expo is an integer
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def extract(s):
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if decoder.match(s) < 0: raise NotANumber
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(a1, b1), (a2, b2), (a3, b3), (a4, b4), (a5, b5) = decoder.regs[1:6]
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sign, intpart, fraction, exppart = \
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s[a1:b1], s[a2:b2], s[a3:b3], s[a5:b5]
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if sign == '+': sign = ''
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if fraction: fraction = fraction[1:]
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if exppart: expo = eval(exppart[1:])
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else: expo = 0
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return sign, intpart, fraction, expo
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# Remove the exponent by changing intpart and fraction
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def unexpo(intpart, fraction, expo):
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if expo > 0: # Move the point left
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f = len(fraction)
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intpart, fraction = intpart + fraction[:expo], fraction[expo:]
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if expo > f:
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intpart = intpart + '0'*(expo-f)
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elif expo < 0: # Move the point right
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i = len(intpart)
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intpart, fraction = intpart[:expo], intpart[expo:] + fraction
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if expo < -i:
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fraction = '0'*(-expo-i) + fraction
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return intpart, fraction
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# Round or extend the fraction to size digs
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def roundfrac(intpart, fraction, digs):
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f = len(fraction)
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if f <= digs:
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return intpart, fraction + '0'*(digs-f)
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i = len(intpart)
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if i+digs < 0:
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return '0'*-digs, ''
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total = intpart + fraction
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nextdigit = total[i+digs]
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if nextdigit >= '5': # Hard case: increment last digit, may have carry!
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n = i + digs - 1
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while n >= 0:
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if total[n] != '9': break
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n = n-1
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else:
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total = '0' + total
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i = i+1
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n = 0
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total = total[:n] + chr(ord(total[n]) + 1) + '0'*(len(total)-n-1)
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intpart, fraction = total[:i], total[i:]
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if digs >= 0:
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return intpart, fraction[:digs]
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else:
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return intpart[:digs] + '0'*-digs, ''
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# Format x as [-]ddd.ddd with 'digs' digits after the point
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# and at least one digit before.
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# If digs <= 0, the point is suppressed.
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def fix(x, digs):
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if type(x) != type(''): x = `x`
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try:
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sign, intpart, fraction, expo = extract(x)
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except NotANumber:
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return x
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intpart, fraction = unexpo(intpart, fraction, expo)
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intpart, fraction = roundfrac(intpart, fraction, digs)
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while intpart and intpart[0] == '0': intpart = intpart[1:]
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if intpart == '': intpart = '0'
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if digs > 0: return sign + intpart + '.' + fraction
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else: return sign + intpart
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# Format x as [-]d.dddE[+-]ddd with 'digs' digits after the point
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# and exactly one digit before.
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# If digs is <= 0, one digit is kept and the point is suppressed.
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def sci(x, digs):
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if type(x) != type(''): x = `x`
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sign, intpart, fraction, expo = extract(x)
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if not intpart:
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while fraction and fraction[0] == '0':
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fraction = fraction[1:]
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expo = expo - 1
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if fraction:
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intpart, fraction = fraction[0], fraction[1:]
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expo = expo - 1
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else:
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intpart = '0'
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else:
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expo = expo + len(intpart) - 1
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intpart, fraction = intpart[0], intpart[1:] + fraction
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digs = max(0, digs)
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intpart, fraction = roundfrac(intpart, fraction, digs)
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if len(intpart) > 1:
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intpart, fraction, expo = \
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intpart[0], intpart[1:] + fraction[:-1], \
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expo + len(intpart) - 1
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s = sign + intpart
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if digs > 0: s = s + '.' + fraction
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e = `abs(expo)`
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e = '0'*(3-len(e)) + e
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if expo < 0: e = '-' + e
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else: e = '+' + e
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return s + 'e' + e
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# Interactive test run
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def test():
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try:
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while 1:
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x, digs = input('Enter (x, digs): ')
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print x, fix(x, digs), sci(x, digs)
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except (EOFError, KeyboardInterrupt):
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pass
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