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to_precision.py
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__author__ = '''
William Rusnack github.com/BebeSparkelSparkel linkedin.com/in/williamrusnack [email protected]
Eric Moyer github.com/epmoyer [email protected]
Thomas Hladish https://github.com/tjhladish [email protected]
'''
from math import floor, log10
def std_notation(value, precision):
'''
standard notation (US version)
ref: http://www.mathsisfun.com/definitions/standard-notation.html
returns a string of value with the proper precision
ex:
std_notation(5, 2) => '5.0'
std_notation(5.36, 2) => '5.4'
std_notation(5360, 2) => '5400'
std_notation(0.05363, 3) => '0.0536'
created by William Rusnack
github.com/BebeSparkelSparkel
linkedin.com/in/williamrusnack/
'''
return to_precision(value, precision, notation='std')
def sci_notation(value, precision, delimiter='e'):
'''
scientific notation
ref: https://www.mathsisfun.com/numbers/scientific-notation.html
returns a string of value with the proper precision and 10s exponent
delimiter is placed between the decimal value and 10s exponent
ex:
sci_notation(123, 1, 'E') => '1E2'
sci_notation(123, 3, 'E') => '1.23E2'
sci_notation(.126, 2, 'E') => '1.3E-1'
created by William Rusnack
github.com/BebeSparkelSparkel
linkedin.com/in/williamrusnack/
'''
return to_precision(value, precision, notation='sci', delimiter=delimiter)
def eng_notation(value, precision, delimiter='e'):
'''
engineering notation
ref: http://www.mathsisfun.com/definitions/engineering-notation.html
returns a string of value with the proper precision and 10s exponent that is divisible by 3
delimiter is placed between the decimal value and 10s exponent
ex:
sci_notation(123, 1, 'E') => '100E0'
sci_notation(1230, 3, 'E') => '1.23E3'
sci_notation(.126, 2, 'E') => '120E-3'
created by William Rusnack
github.com/BebeSparkelSparkel
linkedin.com/in/williamrusnack/
'''
return to_precision(value, precision, notation='eng', delimiter=delimiter)
def auto_notation(value, precision, delimiter='e'):
'''
Automatically selects between standard notation (US version) and scientific notation.
Values in the range 0.001 < abs(value) < 1000 return standard notation.
http://www.mathsisfun.com/definitions/standard-notation.html
https://www.mathsisfun.com/numbers/scientific-notation.html
returns a string of value with the proper precision
ex:
auto_notation(123, 4) => '123.4'
std_notation(1234, 4) => '1.234e3'
'''
return to_precision(value, precision, notation='auto', delimiter=delimiter)
def to_precision(
value,
precision,
notation='auto',
delimiter='e',
auto_limit=3,
strip_zeros=False,
preserve_integer=False):
'''
converts a value to the specified notation and precision
value - any type that can be converted to a float
precision - integer that is greater than zero
notation - string
'auto' - selects standard notation when abs(power) < auto_limit else
returns scientific notation.
'sci' or 'scientific' - returns scientific notation
ref: https://www.mathsisfun.com/numbers/scientific-notation.html
'eng' or 'engineering' - returns engineering notation
ref: http://www.mathsisfun.com/definitions/engineering-notation.html
'std' or 'standard' - returns standard notation
ref: http://www.mathsisfun.com/definitions/standard-notation.html
delimiter - is placed between the decimal value and 10s exponent
auto_limit - integer. When abs(power) exceeds this limit, 'auto'
mode will return scientific notation.
strip_zeros - if true, trailing decimal zeros will be removed.
preserve_integer - if true, 'std' will preserve all digits when returning
values that have no decimal component.
'''
is_neg, sig_digits, dot_power, ten_power = _sci_decompose(value, precision)
if notation == 'auto':
if abs(ten_power) < auto_limit:
converter = _std_notation
else:
converter = _sci_notation
elif notation in ('sci', 'scientific'):
converter = _sci_notation
elif notation in ('eng', 'engineering'):
converter = _eng_notation
elif notation in ('std', 'standard'):
converter = _std_notation
else:
raise ValueError('Unknown notation: ' + str(notation))
return converter(value, precision, delimiter, strip_zeros, preserve_integer)
def _std_notation(value, precision, _, strip_zeros, preserve_integer):
'''
standard notation (US version)
ref: http://www.mathsisfun.com/definitions/standard-notation.html
returns a string of value with the proper precision
strip_zeros - if true, trailing decimal zeros will be removed.
preserve_integer - if true, 'std' will preserve all digits when returning
values that have no decimal component.
'''
sig_digits, power, is_neg = _number_profile(value, precision)
result = ('-' if is_neg else '') + _place_dot(sig_digits, power, strip_zeros)
if preserve_integer and not '.' in result:
# Result was an integer, preserve all digits
result = '{:0.0f}'.format(value)
return result
def _sci_notation(value, precision, delimiter, strip_zeros, _):
'''
scientific notation
ref: https://www.mathsisfun.com/numbers/scientific-notation.html
returns a string of value with the proper precision and 10s exponent
delimiter is placed between the decimal value and 10s exponent
strip_zeros - if true, trailing decimal zeros will be removed.
'''
is_neg, sig_digits, dot_power, ten_power = _sci_decompose(value, precision)
return ('-' if is_neg else '') + _place_dot(sig_digits, dot_power, strip_zeros) + delimiter + str(ten_power)
def _eng_notation(value, precision, delimiter, strip_zeros, _):
'''
engineering notation
ref: http://www.mathsisfun.com/definitions/engineering-notation.html
returns a string of value with the proper precision and 10s exponent that is divisible by 3
delimiter is placed between the decimal value and 10s exponent
strip_zeros - if true, trailing decimal zeros will be removed.
'''
is_neg, sig_digits, dot_power, ten_power = _sci_decompose(value, precision)
eng_power = int(3 * floor(ten_power / 3))
eng_dot = dot_power + ten_power - eng_power
return ('-' if is_neg else '') + _place_dot(sig_digits, eng_dot, strip_zeros) + delimiter + str(eng_power)
def _sci_decompose(value, precision):
'''
returns the properties for to construct a scientific notation number
used in sci_notation and eng_notation
created by William Rusnack
github.com/BebeSparkelSparkel
linkedin.com/in/williamrusnack/
'''
value = float(value)
sig_digits, power, is_neg = _number_profile(value, precision)
dot_power = -(precision - 1)
ten_power = power + precision - 1
return is_neg, sig_digits, dot_power, ten_power
def _place_dot(digits, power, strip_zeros=False):
'''
places the dot in the correct spot in the digits
if the dot is outside the range of the digits zeros will be added
if strip_zeros is set, trailing decimal zeros will be removed
ex:
_place_dot('123', 2, False) => '12300'
_place_dot('123', -2, False) => '1.23'
_place_dot('123', 3, False) => '0.123'
_place_dot('123', 5, False) => '0.00123'
_place_dot('120', 0, False) => '120.'
_place_dot('1200', -2, False) => '12.00'
_place_dot('1200', -2, True ) => '12'
_place_dot('1200', -1, False) => '120.0'
_place_dot('1200', -1, True ) => '120'
created by William Rusnack
github.com/BebeSparkelSparkel
linkedin.com/in/williamrusnack/
'''
if power > 0:
out = digits + '0' * power
elif power < 0:
power = abs(power)
precision = len(digits)
if power < precision:
out = digits[:-power] + '.' + digits[-power:]
else:
out = '0.' + '0' * (power - precision) + digits
else:
out = digits + ('.' if digits[-1] == '0' and len(digits) > 1 else '')
if strip_zeros and '.' in out:
out = out.rstrip('0').rstrip('.')
return out
def _number_profile(value, precision):
'''
returns:
string of significant digits
10s exponent to get the dot to the proper location in the significant digits
bool that's true if value is less than zero else false
created by William Rusnack
github.com/BebeSparkelSparkel
linkedin.com/in/williamrusnack/
contributions by Thomas Hladish
github.com/tjhladish
Issue: github.com/BebeSparkelSparkel/to-precision/issues/5
'''
value = float(value)
is_neg = value < 0
value = abs(value)
if value == 0:
sig_digits = '0' * precision
power = -(1 - precision)
else:
power = -1 * floor(log10(value)) + precision - 1
# issue soved by Thomas Haladish
# github.com/BebeSparkelSparkel/to-precision/issues/5
value_power = value * 10.0**power
if value < 1 and \
floor(log10(int(round(value_power)))) > \
floor(log10(int(value_power))):
power -= 1
sig_digits = str(int(round(value * 10.0**power))) # cannot use value_power because power is changed
return sig_digits, int(-power), is_neg