第5课 Python函数库分类及函数标准库示例

1.Python函数分类
1. 系统库提供内部函数
2. 第三方提供的函数
3. 自定义函数
2. Python函数之系统函数库
函数的调用:实参

 字符函数库help(str)

>>> str='jeepedu'
>>> str.islower()---判断是否全部是小写返回布尔类型
True
>>> str.upper() –将字符串转换成大写
'JEEPEDU'
>>> str.startswith('j')判断字符串是否以某个字符开头
True
>>> str.replace('jeep','java') 将字符串中jeep替换成Java
'javaedu'
>>> str.space() 判断字符串是否为空
>>> str.isspace()
False
	数学函数库
需引入数学库 import math
>>> import math
>>> val=math.sin(3.14/6)
>>> print val
0.499770102643
>>> math.pi
3.141592653589793
>>> val =math.sin(math.pi)/6
>>> print val
2.04107799858e-17
>>> help(math)
Math中的函数
>>> help(math)
Help on built-in module math:

NAME
    math

FILE
    (built-in)

DESCRIPTION
    This module is always available.  It provides access to the
    mathematical functions defined by the C standard.

FUNCTIONS
    acos(...)
        acos(x)
        
        Return the arc cosine (measured in radians) of x.
    
    acosh(...)
        acosh(x)
        
        Return the inverse hyperbolic cosine of x.
    
    asin(...)
        asin(x)
        
        Return the arc sine (measured in radians) of x.
    
    asinh(...)
        asinh(x)
        
        Return the inverse hyperbolic sine of x.
    
    atan(...)
        atan(x)
        
        Return the arc tangent (measured in radians) of x.
    
    atan2(...)
        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(...)
        atanh(x)
        
        Return the inverse hyperbolic tangent of x.
    
    ceil(...)
        ceil(x)
        
        Return the ceiling of x as a float.
        This is the smallest integral value >= x.
    
    copysign(...)
        copysign(x, y)
        
        Return x with the sign of y.
    
    cos(...)
        cos(x)
        
        Return the cosine of x (measured in radians).
    
    cosh(...)
        cosh(x)
        
        Return the hyperbolic cosine of x.
    
    degrees(...)
        degrees(x)
        
        Convert angle x from radians to degrees.
    
    erf(...)
        erf(x)
        
        Error function at x.
    
    erfc(...)
        erfc(x)
        
        Complementary error function at x.
    
    exp(...)
        exp(x)
        
        Return e raised to the power of x.
    
    expm1(...)
        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(...)
        fabs(x)
        
        Return the absolute value of the float x.
    
    factorial(...)
        factorial(x) -> Integral
        
        Find x!. Raise a ValueError if x is negative or non-integral.
    
    floor(...)
        floor(x)
        
        Return the floor of x as a float.
        This is the largest integral value <= x.
    
    fmod(...)
        fmod(x, y)
        
        Return fmod(x, y), according to platform C.  x % y may differ.
    
    frexp(...)
        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(...)
        fsum(iterable)
        
        Return an accurate floating point sum of values in the iterable.
        Assumes IEEE-754 floating point arithmetic.
    
    gamma(...)
        gamma(x)
        
        Gamma function at x.
    
    hypot(...)
        hypot(x, y)
        
        Return the Euclidean distance, sqrt(x*x + y*y).
    
    isinf(...)
        isinf(x) -> bool
        
        Check if float x is infinite (positive or negative).
    
    isnan(...)
        isnan(x) -> bool
        
        Check if float x is not a number (NaN).
    
    ldexp(...)
        ldexp(x, i)
        
        Return x * (2**i).
    
    lgamma(...)
        lgamma(x)
        
        Natural logarithm of absolute value of Gamma function at x.
    
    log(...)
        log(x[, base])
        
        Return the logarithm of x to the given base.
        If the base not specified, returns the natural logarithm (base e) of x.
    
    log10(...)
        log10(x)
        
        Return the base 10 logarithm of x.
    
    log1p(...)
        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.
    
    modf(...)
        modf(x)
        
        Return the fractional and integer parts of x.  Both results carry the sign
        of x and are floats.
    
    pow(...)
        pow(x, y)
        
        Return x**y (x to the power of y).
    
    radians(...)
        radians(x)
        
        Convert angle x from degrees to radians.
    
    sin(...)
        sin(x)
        
        Return the sine of x (measured in radians).
    
    sinh(...)
        sinh(x)
        
        Return the hyperbolic sine of x.
    
    sqrt(...)
        sqrt(x)
        
        Return the square root of x.
    
    tan(...)
        tan(x)
        
        Return the tangent of x (measured in radians).
    
    tanh(...)
        tanh(x)
        
        Return the hyperbolic tangent of x.
    
    trunc(...)
        trunc(x:Real) -> Integral
        
        Truncates x to the nearest Integral toward 0. Uses the __trunc__ magic method.

DATA
    e = 2.718281828459045
pi = 3.141592653589793
>>> 3*3*3
27
>>> 3**4
81
>>> math.pow(3,7)
操作系统库
>>> import os     
>>> os.getcwd()    ---获得当前的工作路径
'E:\\Program Files\\Python27'
>>> currentdir=os.getcwd()
>>> print currentdir
E:\Program Files\Python27
>>> help(os.listdir)
Help on built-in function listdir in module nt:

listdir(...)
    listdir(path) -> list_of_strings
    
    Return a list containing the names of the entries in the directory.
    
        path: path of directory to list
    
    The list is in arbitrary order.  It does not include the special
entries '.' and '..' even if they are present in the directory.
>>> ldirs=os.listdir(currentdir)
>>> print ldirs
['DLLs', 'Doc', 'include', 'Lib', 'libs', 'LICENSE.txt', 'NEWS.txt', 'python.exe', 'pythonw.exe', 'README.txt', 'Scripts', 'tcl', 'Tools']
	网络编程库
>>> import socket
>>> baiduuip=socket.gethostbyname('www.baidu.com')
>>> print baiduuip
180.97.33.108
>>> help(socket.gethostbyname)
Help on built-in function gethostbyname in module _socket:

gethostbyname(...)
    gethostbyname(host) -> address
    
    Return the IP address (a string of the form '255.255.255.255') for a host.