mirror of
https://github.com/python/cpython.git
synced 2025-10-31 10:26:02 +00:00
142 lines
4.5 KiB
Python
142 lines
4.5 KiB
Python
"""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
|
|
|
|
__all__ = ["fix","sci","NotANumber"]
|
|
|
|
# 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
|