142 lines
4.5 KiB
Python
142 lines
4.5 KiB
Python
"""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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"""
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import re
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__all__ = ["fix","sci","NotANumber"]
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# Compiled regular expression to "decode" a number
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decoder = re.compile(r'^([-+]?)0*(\d*)((?:\.\d*)?)(([eE][-+]?\d+)?)$')
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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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# \4 exponent part (empty or begins with 'e' or 'E')
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try:
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class NotANumber(ValueError):
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pass
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except TypeError:
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NotANumber = 'fpformat.NotANumber'
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def extract(s):
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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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res = decoder.match(s)
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if res is None: raise NotANumber, s
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sign, intpart, fraction, exppart = res.group(1,2,3,4)
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if sign == '+': sign = ''
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if fraction: fraction = fraction[1:]
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if exppart: expo = int(exppart[1:])
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else: expo = 0
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return sign, intpart, fraction, expo
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def unexpo(intpart, fraction, expo):
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"""Remove the exponent by changing intpart and fraction."""
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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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def roundfrac(intpart, fraction, digs):
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"""Round or extend the fraction to size 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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def fix(x, 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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if type(x) != type(''): x = repr(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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def sci(x, digs):
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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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if type(x) != type(''): x = repr(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 = repr(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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def test():
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"""Interactive test run."""
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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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