python中的函数---函数应用

　　每种编程语言中，都需要函数的参与，python同样也不例外。函数是集成的子程序，是算法实现的最小方法单位，是完成基本操作的手段的集合。编程中能够灵活应用函数，提高程序设计的简单化；实现代码应用的复用化；提升代码阅读的清晰化；加强代码开发的强健化；加快代码开发的效率化；增强团队开发的便利化；降低程序理解的复杂化；减少代码存储的减少化。总之，函数就是为实现功能或操作的独立功能块，可以返回也可以不返回值，可以返回一个值，可以返回多个值等。

　　一、使用内置函数：

　　1、简单内置函数的应用：

　　查看帮助，获取函数的功能和函数的参数等信息，例如想查看abs的函数信息

　　首先：通过命令终端输入python进入python交互模式

　　接着：使用help函数，参数为abs获取帮助，输入help(abs)

　　然后：查看帮助信息，本例中具体为　　

Help on built-in function abs in module builtins:

abs(x, /)
    Return the absolute value of the argument.
(END)

　　意思很简单，具体为：返回参数的绝对值

　　最后：使用函数，本例中如果：

>>> abs(9, -2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: abs() takes exactly one argument (2 given)
>>> abs(-2)
2

　　如果输入的参数有两个，则出现错误，否则就是正确的。

　　2、稍微复杂内置函数的应用：　　

　　查看帮助，获取函数的功能和函数的参数等信息，例如想查看max的函数信息

　　首先：通过命令终端输入python进入python交互模式

　　接着：导入math模块，使用help函数，参数为max获取帮助，输入help(max)

　　然后：查看帮助信息，本例中具体为

Help on built-in function max in module builtins:

max(...)
    max(iterable, *[, default=obj, key=func]) -> value
    max(arg1, arg2, *args, *[, key=func]) -> value

    With a single iterable argument, return its biggest item. The
    default keyword-only argument specifies an object to return if
    the provided iterable is empty.
    With two or more arguments, return the largest argument.
(END)

　　意思很简单，具体为：返回参数的最大值

　　最后：使用函数，本例中如果：

>>> import math
>>> print('45, 23, 36, 21, 9, 99中最大的数为：', max(45, 23, 36, 21, 9, 99))
45, 23, 36, 21, 9, 99中最大的数为： 99

　　可以查看模块帮助：

Help on module math:

NAME
    math

MODULE REFERENCE
    https://docs.python.org/3.8/library/math

    The following documentation is automatically generated from the Python
    source files.  It may be incomplete, incorrect or include features that
    are considered implementation detail and may vary between Python
    implementations.  When in doubt, consult the module reference at the
    location listed above.

DESCRIPTION
    This module provides access to the mathematical functions
    defined by the C standard.

FUNCTIONS
    acos(x, /)
        Return the arc cosine (measured in radians) of x.

    acosh(x, /)
        Return the inverse hyperbolic cosine of x.

    asin(x, /)
        Return the arc sine (measured in radians) of x.

    asinh(x, /)
        Return the inverse hyperbolic sine of x.

atan(x, /)
        Return the arc tangent (measured in radians) of x.

    atan2(y, x, /)
        Return the arc tangent (measured in radians) of y/x.

        Unlike atan(y/x), the signs of both x and y are considered.

    atanh(x, /)
        Return the inverse hyperbolic tangent of x.

    ceil(x, /)
        Return the ceiling of x as an Integral.

        This is the smallest integer >= x.

    comb(n, k, /)
        Number of ways to choose k items from n items without repetition and without order.

        Evaluates to n! / (k! * (n - k)!) when k <= n and evaluates
        to zero when k > n.

        Also called the binomial coefficient because it is equivalent
        to the coefficient of k-th term in polynomial expansion of the
        expression (1 + x)**n.

        Raises TypeError if either of the arguments are not integers.
        Raises ValueError if either of the arguments are negative.

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.

    cos(x, /)
        Return the cosine of x (measured in radians).

    cosh(x, /)
        Return the hyperbolic cosine of x.

    degrees(x, /)
        Convert angle x from radians to degrees.

    dist(p, q, /)
        Return the Euclidean distance between two points p and q.

        The points should be specified as sequences (or iterables) of
        coordinates.  Both inputs must have the same dimension.

        Roughly equivalent to:
            sqrt(sum((px - qx) ** 2.0 for px, qx in zip(p, q)))

    erf(x, /)
        Error function at x.

    erfc(x, /)
        Complementary error function at x.

 exp(x, /)
        Return e raised to the power of x.

    expm1(x, /)
        Return exp(x)-1.

        This function avoids the loss of precision involved in the direct evaluation of exp(x)-1 for small x.

    fabs(x, /)
        Return the absolute value of the float x.

    factorial(x, /)
        Find x!.

        Raise a ValueError if x is negative or non-integral.

    floor(x, /)
        Return the floor of x as an Integral.

        This is the largest integer <= x.

    fmod(x, y, /)
        Return fmod(x, y), according to platform C.

        x % y may differ.

    frexp(x, /)
        Return the mantissa and exponent of x, as pair (m, e).

        m is a float and e is an int, such that x = m * 2.**e.
        If x is 0, m and e are both 0.  Else 0.5 <= abs(m) < 1.0.

fsum(seq, /)
        Return an accurate floating point sum of values in the iterable seq.

        Assumes IEEE-754 floating point arithmetic.

    gamma(x, /)
        Gamma function at x.

    gcd(x, y, /)
        greatest common divisor of x and y

    hypot(...)
        hypot(*coordinates) -> value

        Multidimensional Euclidean distance from the origin to a point.

        Roughly equivalent to:
            sqrt(sum(x**2 for x in coordinates))

        For a two dimensional point (x, y), gives the hypotenuse
        using the Pythagorean theorem:  sqrt(x*x + y*y).

        For example, the hypotenuse of a 3/4/5 right triangle is:

            >>> hypot(3.0, 4.0)
            5.0

    isclose(a, b, *, rel_tol=1e-09, abs_tol=0.0)
        Determine whether two floating point numbers are close in value.
    rel_tol
            maximum difference for being considered "close", relative to the
            magnitude of the input values
          abs_tol
            maximum difference for being considered "close", regardless of the
            magnitude of the input values

        Return True if a is close in value to b, and False otherwise.

        For the values to be considered close, the difference between them
        must be smaller than at least one of the tolerances.

        -inf, inf and NaN behave similarly to the IEEE 754 Standard.  That
        is, NaN is not close to anything, even itself.  inf and -inf are
        only close to themselves.

    isfinite(x, /)
        Return True if x is neither an infinity nor a NaN, and False otherwise.

    isinf(x, /)
        Return True if x is a positive or negative infinity, and False otherwise.

    isnan(x, /)
        Return True if x is a NaN (not a number), and False otherwise.

    isqrt(n, /)
        Return the integer part of the square root of the input.

    ldexp(x, i, /)
        Return x * (2**i).

        This is essentially the inverse of frexp().

    lgamma(x, /)
        Natural logarithm of absolute value of Gamma function at x.

    log(...)
        log(x, [base=math.e])
        Return the logarithm of x to the given base.

        If the base not specified, returns the natural logarithm (base e) of x.

    log10(x, /)
        Return the base 10 logarithm of x.

    log1p(x, /)
        Return the natural logarithm of 1+x (base e).

        The result is computed in a way which is accurate for x near zero.

    log2(x, /)
        Return the base 2 logarithm of x.

    modf(x, /)
        Return the fractional and integer parts of x.

        Both results carry the sign of x and are floats.

    perm(n, k=None, /)
        Number of ways to choose k items from n items without repetition and with order.

        Evaluates to n! / (n - k)! when k <= n and evaluates
        to zero when k > 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.
        Raises ValueError if either of the arguments are negative.

    pow(x, y, /)
        Return x**y (x to the power of y).

    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.

 radians(x, /)
        Convert angle x from degrees to radians.

    remainder(x, y, /)
        Difference between x and the closest integer multiple of y.

        Return x - n*y where n*y is the closest integer multiple of y.
        In the case where x is exactly halfway between two multiples of
        y, the nearest even value of n is used. The result is always exact.

    sin(x, /)
        Return the sine of x (measured in radians).

    sinh(x, /)
        Return the hyperbolic sine of x.

    sqrt(x, /)
        Return the square root of x.

    tan(x, /)
        Return the tangent of x (measured in radians).

    tanh(x, /)
        Return the hyperbolic tangent of x.

    trunc(x, /)
        Truncates the Real x to the nearest Integral toward 0.

        Uses the __trunc__ magic method.

DATA
    e = 2.718281828459045
    inf = inf
    nan = nan
    pi = 3.141592653589793
    tau = 6.283185307179586

FILE
    /usr/lib/python3.8/lib-dynload/math.cpython-38-aarch64-linux-gnu.so

　　一下子可以查看模块中的所有函数。

　　3、随机函数需要导入random

print('return item from list:', random.choice(['spring', 'summer','autumn', 'winter']))
return item from list: autumn
>>> print('return item from list:', random.choice((27, 95, 68, 75,44)))
return item from list: 27
>>> print('return item from list:', random.choice('hello world!'))
return item from list: o
>>> print('return item from list:', random.sample(['spring', 'summer','autumn', 'winter'], 2))
return item from list: ['spring', 'summer']
>>> print('return item from list:', random.sample((27, 95, 68, 75,44),2))
return item from list: [44, 75]
>>> print('return item from list:', random.sample('hello world!', 5))
return item from list: ['r', '!', 'o', 'w', 'o']
>>> print('return item from list:', random.randint(1, 100))
return item from list: 29
>>> print('return item from list:', random.randint(50, 100))
return item from list: 55
>>> print('return item from list:', random.uniform(50, 100))
return item from list: 57.86905642417648
print('return item from list:', random.random())return item from list: 0.059261740874653634
>>> random.seed(1000)
>>> print('return item from list:', random.random())
return item from list: 0.7773566427005639
>>> random.seed('helloworld', 2)
>>> print('return item from list:', random.random())
return item from list: 0.7513369593825964

　　4、三角函数需要导入math

>>> print('acos(0.5):', math.acos(0.5))
acos(0.5): 1.0471975511965979
>>> print('cos(math.pi/4):', math.cos(math.pi/4))
cos(math.pi/4): 0.7071067811865476
>>> print('sin(math.pi/4):', math.sin(math.pi/4))
sin(math.pi/4): 0.7071067811865475
>>> print('tan(math.pi/4):', math.tan(math.pi/4))
tan(math.pi/4): 0.9999999999999999
>>> print('atan(1):', math.atan(1))
atan(1): 0.7853981633974483

　　5、字符串函数需要导入不用导入