math
--- 數學函式¶
This module provides access to the mathematical functions defined by the C standard.
These functions cannot be used with complex numbers; use the functions of the
same name from the cmath
module if you require support for complex
numbers. The distinction between functions which support complex numbers and
those which don't is made since most users do not want to learn quite as much
mathematics as required to understand complex numbers. Receiving an exception
instead of a complex result allows earlier detection of the unexpected complex
number used as a parameter, so that the programmer can determine how and why it
was generated in the first place.
The following functions are provided by this module. Except when explicitly noted otherwise, all return values are floats.
Number-theoretic and representation functions¶
- math.ceil(x)¶
Return the ceiling of x, the smallest integer greater than or equal to x. If x is not a float, delegates to
x.__ceil__
, which should return anIntegral
value.
- math.comb(n, k)¶
Return the number of ways to choose k items from n items without repetition and without order.
Evaluates to
n! / (k! * (n - k)!)
whenk <= n
and evaluates to zero whenk > n
.Also called the binomial coefficient because it is equivalent to the coefficient of k-th term in polynomial expansion of
(1 + x)ⁿ
.Raises
TypeError
if either of the arguments are not integers. RaisesValueError
if either of the arguments are negative.在 3.8 版新加入.
- math.copysign(x, y)¶
Return a float with the magnitude (absolute value) of x but the sign of y. On platforms that support signed zeros,
copysign(1.0, -0.0)
returns -1.0.
- math.fabs(x)¶
Return the absolute value of x.
- math.factorial(n)¶
Return n factorial as an integer. Raises
ValueError
if n is not integral or is negative.在 3.9 版之後被棄用: Accepting floats with integral values (like
5.0
) is deprecated.
- math.floor(x)¶
Return the floor of x, the largest integer less than or equal to x. If x is not a float, delegates to
x.__floor__
, which should return anIntegral
value.
- math.fmod(x, y)¶
Return
fmod(x, y)
, as defined by the platform C library. Note that the Python expressionx % y
may not return the same result. The intent of the C standard is thatfmod(x, y)
be exactly (mathematically; to infinite precision) equal tox - n*y
for some integer n such that the result has the same sign as x and magnitude less thanabs(y)
. Python'sx % y
returns a result with the sign of y instead, and may not be exactly computable for float arguments. For example,fmod(-1e-100, 1e100)
is-1e-100
, but the result of Python's-1e-100 % 1e100
is1e100-1e-100
, which cannot be represented exactly as a float, and rounds to the surprising1e100
. For this reason, functionfmod()
is generally preferred when working with floats, while Python'sx % y
is preferred when working with integers.
- math.frexp(x)¶
Return the mantissa and exponent of x as the pair
(m, e)
. m is a float and e is an integer such thatx == m * 2**e
exactly. If x is zero, returns(0.0, 0)
, otherwise0.5 <= abs(m) < 1
. This is used to "pick apart" the internal representation of a float in a portable way.
- math.fsum(iterable)¶
Return an accurate floating point sum of values in the iterable. Avoids loss of precision by tracking multiple intermediate partial sums:
>>> sum([.1, .1, .1, .1, .1, .1, .1, .1, .1, .1]) 0.9999999999999999 >>> fsum([.1, .1, .1, .1, .1, .1, .1, .1, .1, .1]) 1.0
The algorithm's accuracy depends on IEEE-754 arithmetic guarantees and the typical case where the rounding mode is half-even. On some non-Windows builds, the underlying C library uses extended precision addition and may occasionally double-round an intermediate sum causing it to be off in its least significant bit.
For further discussion and two alternative approaches, see the ASPN cookbook recipes for accurate floating point summation.
- math.gcd(*integers)¶
Return the greatest common divisor of the specified integer arguments. If any of the arguments is nonzero, then the returned value is the largest positive integer that is a divisor of all arguments. If all arguments are zero, then the returned value is
0
.gcd()
without arguments returns0
.在 3.5 版新加入.
在 3.9 版的變更: Added support for an arbitrary number of arguments. Formerly, only two arguments were supported.
- math.isclose(a, b, *, rel_tol=1e-09, abs_tol=0.0)¶
Return
True
if the values a and b are close to each other andFalse
otherwise.Whether or not two values are considered close is determined according to given absolute and relative tolerances.
rel_tol is the relative tolerance -- it is the maximum allowed difference between a and b, relative to the larger absolute value of a or b. For example, to set a tolerance of 5%, pass
rel_tol=0.05
. The default tolerance is1e-09
, which assures that the two values are the same within about 9 decimal digits. rel_tol must be greater than zero.abs_tol is the minimum absolute tolerance -- useful for comparisons near zero. abs_tol must be at least zero.
If no errors occur, the result will be:
abs(a-b) <= max(rel_tol * max(abs(a), abs(b)), abs_tol)
.The IEEE 754 special values of
NaN
,inf
, and-inf
will be handled according to IEEE rules. Specifically,NaN
is not considered close to any other value, includingNaN
.inf
and-inf
are only considered close to themselves.在 3.5 版新加入.
也參考
PEP 485 -- A function for testing approximate equality
- math.isfinite(x)¶
Return
True
if x is neither an infinity nor a NaN, andFalse
otherwise. (Note that0.0
is considered finite.)在 3.2 版新加入.
- math.isinf(x)¶
Return
True
if x is a positive or negative infinity, andFalse
otherwise.
- math.isnan(x)¶
Return
True
if x is a NaN (not a number), andFalse
otherwise.
- math.isqrt(n)¶
Return the integer square root of the nonnegative integer n. This is the floor of the exact square root of n, or equivalently the greatest integer a such that a² ≤ n.
For some applications, it may be more convenient to have the least integer a such that n ≤ a², or in other words the ceiling of the exact square root of n. For positive n, this can be computed using
a = 1 + isqrt(n - 1)
.在 3.8 版新加入.
- math.lcm(*integers)¶
Return the least common multiple of the specified integer arguments. If all arguments are nonzero, then the returned value is the smallest positive integer that is a multiple of all arguments. If any of the arguments is zero, then the returned value is
0
.lcm()
without arguments returns1
.在 3.9 版新加入.
- math.modf(x)¶
Return the fractional and integer parts of x. Both results carry the sign of x and are floats.
- math.nextafter(x, y)¶
Return the next floating-point value after x towards y.
If x is equal to y, return y.
範例：
math.nextafter(x, math.inf)
goes up: towards positive infinity.math.nextafter(x, -math.inf)
goes down: towards minus infinity.math.nextafter(x, 0.0)
goes towards zero.math.nextafter(x, math.copysign(math.inf, x))
goes away from zero.
另請參閱
math.ulp()
。在 3.9 版新加入.
- math.perm(n, k=None)¶
Return the number of ways to choose k items from n items without repetition and with order.
Evaluates to
n! / (n - k)!
whenk <= n
and evaluates to zero whenk > n
.If k is not specified or is None, then k defaults to n and the function returns
n!
.Raises
TypeError
if either of the arguments are not integers. RaisesValueError
if either of the arguments are negative.在 3.8 版新加入.
- math.prod(iterable, *, start=1)¶
Calculate the product of all the elements in the input iterable. The default start value for the product is
1
.When the iterable is empty, return the start value. This function is intended specifically for use with numeric values and may reject non-numeric types.
在 3.8 版新加入.
- math.remainder(x, y)¶
Return the IEEE 754-style remainder of x with respect to y. For finite x and finite nonzero y, this is the difference
x - n*y
, wheren
is the closest integer to the exact value of the quotientx / y
. Ifx / y
is exactly halfway between two consecutive integers, the nearest even integer is used forn
. The remainderr = remainder(x, y)
thus always satisfiesabs(r) <= 0.5 * abs(y)
.Special cases follow IEEE 754: in particular,
remainder(x, math.inf)
is x for any finite x, andremainder(x, 0)
andremainder(math.inf, x)
raiseValueError
for any non-NaN x. If the result of the remainder operation is zero, that zero will have the same sign as x.On platforms using IEEE 754 binary floating-point, the result of this operation is always exactly representable: no rounding error is introduced.
在 3.7 版新加入.
- math.trunc(x)¶
Return x with the fractional part removed, leaving the integer part. This rounds toward 0:
trunc()
is equivalent tofloor()
for positive x, and equivalent toceil()
for negative x. If x is not a float, delegates tox.__trunc__
, which should return anIntegral
value.
- math.ulp(x)¶
Return the value of the least significant bit of the float x:
If x is a NaN (not a number), return x.
If x is negative, return
ulp(-x)
.If x is a positive infinity, return x.
If x is equal to zero, return the smallest positive denormalized representable float (smaller than the minimum positive normalized float,
sys.float_info.min
).If x is equal to the largest positive representable float, return the value of the least significant bit of x, such that the first float smaller than x is
x - ulp(x)
.Otherwise (x is a positive finite number), return the value of the least significant bit of x, such that the first float bigger than x is
x + ulp(x)
.
ULP stands for "Unit in the Last Place".
See also
math.nextafter()
andsys.float_info.epsilon
.在 3.9 版新加入.
Note that frexp()
and modf()
have a different call/return pattern
than their C equivalents: they take a single argument and return a pair of
values, rather than returning their second return value through an 'output
parameter' (there is no such thing in Python).
For the ceil()
, floor()
, and modf()
functions, note that all
floating-point numbers of sufficiently large magnitude are exact integers.
Python floats typically carry no more than 53 bits of precision (the same as the
platform C double type), in which case any float x with abs(x) >= 2**52
necessarily has no fractional bits.
Power and logarithmic functions¶
- math.cbrt(x)¶
Return the cube root of x.
在 3.11 版新加入.
- math.exp(x)¶
Return e raised to the power x, where e = 2.718281... is the base of natural logarithms. This is usually more accurate than
math.e ** x
orpow(math.e, x)
.
- math.exp2(x)¶
Return 2 raised to the power x.
在 3.11 版新加入.
- math.expm1(x)¶
Return e raised to the power x, minus 1. Here e is the base of natural logarithms. For small floats x, the subtraction in
exp(x) - 1
can result in a significant loss of precision; theexpm1()
function provides a way to compute this quantity to full precision:>>> from math import exp, expm1 >>> exp(1e-5) - 1 # gives result accurate to 11 places 1.0000050000069649e-05 >>> expm1(1e-5) # result accurate to full precision 1.0000050000166668e-05
在 3.2 版新加入.
- math.log(x[, base])¶
With one argument, return the natural logarithm of x (to base e).
With two arguments, return the logarithm of x to the given base, calculated as
log(x)/log(base)
.
- math.log1p(x)¶
Return the natural logarithm of 1+x (base e). The result is calculated in a way which is accurate for x near zero.
- math.log2(x)¶
Return the base-2 logarithm of x. This is usually more accurate than
log(x, 2)
.在 3.3 版新加入.
也參考
int.bit_length()
returns the number of bits necessary to represent an integer in binary, excluding the sign and leading zeros.
- math.log10(x)¶
Return the base-10 logarithm of x. This is usually more accurate than
log(x, 10)
.
- math.pow(x, y)¶
Return
x
raised to the powery
. Exceptional cases follow the IEEE 754 standard as far as possible. In particular,pow(1.0, x)
andpow(x, 0.0)
always return1.0
, even whenx
is a zero or a NaN. If bothx
andy
are finite,x
is negative, andy
is not an integer thenpow(x, y)
is undefined, and raisesValueError
.Unlike the built-in
**
operator,math.pow()
converts both its arguments to typefloat
. Use**
or the built-inpow()
function for computing exact integer powers.在 3.11 版的變更: The special cases
pow(0.0, -inf)
andpow(-0.0, -inf)
were changed to returninf
instead of raisingValueError
, for consistency with IEEE 754.
- math.sqrt(x)¶
Return the square root of x.
Trigonometric functions¶
- math.acos(x)¶
Return the arc cosine of x, in radians. The result is between
0
andpi
.
- math.asin(x)¶
Return the arc sine of x, in radians. The result is between
-pi/2
andpi/2
.
- math.atan(x)¶
Return the arc tangent of x, in radians. The result is between
-pi/2
andpi/2
.
- math.atan2(y, x)¶
Return
atan(y / x)
, in radians. The result is between-pi
andpi
. The vector in the plane from the origin to point(x, y)
makes this angle with the positive X axis. The point ofatan2()
is that the signs of both inputs are known to it, so it can compute the correct quadrant for the angle. For example,atan(1)
andatan2(1, 1)
are bothpi/4
, butatan2(-1, -1)
is-3*pi/4
.
- math.cos(x)¶
Return the cosine of x radians.
- math.dist(p, q)¶
Return the Euclidean distance between two points p and q, each given as a sequence (or iterable) of coordinates. The two points must have the same dimension.
Roughly equivalent to:
sqrt(sum((px - qx) ** 2.0 for px, qx in zip(p, q)))
在 3.8 版新加入.
- math.hypot(*coordinates)¶
Return the Euclidean norm,
sqrt(sum(x**2 for x in coordinates))
. This is the length of the vector from the origin to the point given by the coordinates.For a two dimensional point
(x, y)
, this is equivalent to computing the hypotenuse of a right triangle using the Pythagorean theorem,sqrt(x*x + y*y)
.在 3.8 版的變更: Added support for n-dimensional points. Formerly, only the two dimensional case was supported.
在 3.10 版的變更: Improved the algorithm's accuracy so that the maximum error is under 1 ulp (unit in the last place). More typically, the result is almost always correctly rounded to within 1/2 ulp.
- math.sin(x)¶
Return the sine of x radians.
- math.tan(x)¶
Return the tangent of x radians.
Angular conversion¶
- math.degrees(x)¶
Convert angle x from radians to degrees.
- math.radians(x)¶
Convert angle x from degrees to radians.
Hyperbolic functions¶
Hyperbolic functions are analogs of trigonometric functions that are based on hyperbolas instead of circles.
- math.acosh(x)¶
Return the inverse hyperbolic cosine of x.
- math.asinh(x)¶
Return the inverse hyperbolic sine of x.
- math.atanh(x)¶
Return the inverse hyperbolic tangent of x.
- math.cosh(x)¶
Return the hyperbolic cosine of x.
- math.sinh(x)¶
Return the hyperbolic sine of x.
- math.tanh(x)¶
Return the hyperbolic tangent of x.
Special functions¶
- math.erf(x)¶
Return the error function at x.
The
erf()
function can be used to compute traditional statistical functions such as the cumulative standard normal distribution:def phi(x): 'Cumulative distribution function for the standard normal distribution' return (1.0 + erf(x / sqrt(2.0))) / 2.0
在 3.2 版新加入.
- math.erfc(x)¶
Return the complementary error function at x. The complementary error function is defined as
1.0 - erf(x)
. It is used for large values of x where a subtraction from one would cause a loss of significance.在 3.2 版新加入.
- math.gamma(x)¶
Return the Gamma function at x.
在 3.2 版新加入.
- math.lgamma(x)¶
Return the natural logarithm of the absolute value of the Gamma function at x.
在 3.2 版新加入.
常數¶
- math.pi¶
The mathematical constant π = 3.141592..., to available precision.
- math.e¶
The mathematical constant e = 2.718281..., to available precision.
- math.tau¶
The mathematical constant τ = 6.283185..., to available precision. Tau is a circle constant equal to 2π, the ratio of a circle's circumference to its radius. To learn more about Tau, check out Vi Hart's video Pi is (still) Wrong, and start celebrating Tau day by eating twice as much pie!
在 3.6 版新加入.
- math.inf¶
A floating-point positive infinity. (For negative infinity, use
-math.inf
.) Equivalent to the output offloat('inf')
.在 3.5 版新加入.
- math.nan¶
A floating-point "not a number" (NaN) value. Equivalent to the output of
float('nan')
. Due to the requirements of the IEEE-754 standard,math.nan
andfloat('nan')
are not considered to equal to any other numeric value, including themselves. To check whether a number is a NaN, use theisnan()
function to test for NaNs instead ofis
or==
. Example:>>> import math >>> math.nan == math.nan False >>> float('nan') == float('nan') False >>> math.isnan(math.nan) True >>> math.isnan(float('nan')) True
在 3.5 版新加入.
在 3.11 版的變更: It is now always available.
CPython 實作細節： The math
module consists mostly of thin wrappers around the platform C
math library functions. Behavior in exceptional cases follows Annex F of
the C99 standard where appropriate. The current implementation will raise
ValueError
for invalid operations like sqrt(-1.0)
or log(0.0)
(where C99 Annex F recommends signaling invalid operation or divide-by-zero),
and OverflowError
for results that overflow (for example,
exp(1000.0)
). A NaN will not be returned from any of the functions
above unless one or more of the input arguments was a NaN; in that case,
most functions will return a NaN, but (again following C99 Annex F) there
are some exceptions to this rule, for example pow(float('nan'), 0.0)
or
hypot(float('nan'), float('inf'))
.
Note that Python makes no effort to distinguish signaling NaNs from quiet NaNs, and behavior for signaling NaNs remains unspecified. Typical behavior is to treat all NaNs as though they were quiet.
也參考
cmath
模組Complex number versions of many of these functions.