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"""General floating point formatting functions.
Functions:
fix(x, digits_behind)
sci(x, digits_behind)
Each takes a number or a string and a number of digits as arguments.
Parameters:
x: number to be formatted; or a string resembling a number
digits_behind: number of digits behind the decimal point
"""
import re
# Compiled regular expression to "decode" a number
decoder = re.compile(r'^([-+]?)0*(\d*)((?:\.\d*)?)(([eE][-+]?\d+)?)$')
# \0 the whole thing
# \1 leading sign or empty
# \2 digits left of decimal point
# \3 fraction (empty or begins with point)
# \4 exponent part (empty or begins with 'e' or 'E')
try:
class NotANumber(ValueError):
pass
except TypeError:
NotANumber = 'fpformat.NotANumber'
def extract(s):
"""Return (sign, intpart, fraction, expo) or raise an exception:
sign is '+' or '-'
intpart is 0 or more digits beginning with a nonzero
fraction is 0 or more digits
expo is an integer"""
res = decoder.match(s)
if res is None: raise NotANumber, s
sign, intpart, fraction, exppart = res.group(1,2,3,4)
if sign == '+': sign = ''
if fraction: fraction = fraction[1:]
if exppart: expo = int(exppart[1:])
else: expo = 0
return sign, intpart, fraction, expo
def unexpo(intpart, fraction, expo):
"""Remove the exponent by changing intpart and fraction."""
if expo > 0: # Move the point left
f = len(fraction)
intpart, fraction = intpart + fraction[:expo], fraction[expo:]
if expo > f:
intpart = intpart + '0'*(expo-f)
elif expo < 0: # Move the point right
i = len(intpart)
intpart, fraction = intpart[:expo], intpart[expo:] + fraction
if expo < -i:
fraction = '0'*(-expo-i) + fraction
return intpart, fraction
def roundfrac(intpart, fraction, digs):
"""Round or extend the fraction to size digs."""
f = len(fraction)
if f <= digs:
return intpart, fraction + '0'*(digs-f)
i = len(intpart)
if i+digs < 0:
return '0'*-digs, ''
total = intpart + fraction
nextdigit = total[i+digs]
if nextdigit >= '5': # Hard case: increment last digit, may have carry!
n = i + digs - 1
while n >= 0:
if total[n] != '9': break
n = n-1
else:
total = '0' + total
i = i+1
n = 0
total = total[:n] + chr(ord(total[n]) + 1) + '0'*(len(total)-n-1)
intpart, fraction = total[:i], total[i:]
if digs >= 0:
return intpart, fraction[:digs]
else:
return intpart[:digs] + '0'*-digs, ''
def fix(x, digs):
"""Format x as [-]ddd.ddd with 'digs' digits after the point
and at least one digit before.
If digs <= 0, the point is suppressed."""
if type(x) != type(''): x = `x`
try:
sign, intpart, fraction, expo = extract(x)
except NotANumber:
return x
intpart, fraction = unexpo(intpart, fraction, expo)
intpart, fraction = roundfrac(intpart, fraction, digs)
while intpart and intpart[0] == '0': intpart = intpart[1:]
if intpart == '': intpart = '0'
if digs > 0: return sign + intpart + '.' + fraction
else: return sign + intpart
def sci(x, digs):
"""Format x as [-]d.dddE[+-]ddd with 'digs' digits after the point
and exactly one digit before.
If digs is <= 0, one digit is kept and the point is suppressed."""
if type(x) != type(''): x = `x`
sign, intpart, fraction, expo = extract(x)
if not intpart:
while fraction and fraction[0] == '0':
fraction = fraction[1:]
expo = expo - 1
if fraction:
intpart, fraction = fraction[0], fraction[1:]
expo = expo - 1
else:
intpart = '0'
else:
expo = expo + len(intpart) - 1
intpart, fraction = intpart[0], intpart[1:] + fraction
digs = max(0, digs)
intpart, fraction = roundfrac(intpart, fraction, digs)
if len(intpart) > 1:
intpart, fraction, expo = \
intpart[0], intpart[1:] + fraction[:-1], \
expo + len(intpart) - 1
s = sign + intpart
if digs > 0: s = s + '.' + fraction
e = `abs(expo)`
e = '0'*(3-len(e)) + e
if expo < 0: e = '-' + e
else: e = '+' + e
return s + 'e' + e
def test():
"""Interactive test run."""
try:
while 1:
x, digs = input('Enter (x, digs): ')
print x, fix(x, digs), sci(x, digs)
except (EOFError, KeyboardInterrupt):
pass
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