Python Cookbook 2 number Date time (2)

5. Conversion of bytes to large integers

#拥有128位长的16个元素的字节字符串. >>> data = B ' \x00\x124v\x00x\x90\xab\x00\xcd\xef\x01\x00#\x004 ' >>> len (data) 16 resolves the bytes to an integer, using the The Int.from_bytes () method # uses only the low-level arrangement with the python3# byte order rule (little or big) to specify only the byte when the integer is built. >>> int.from_bytes (data, ' little ') 69120565665751139577663547927094891008>>> int.from_bytes (data , ' big ') 94522842520747284487117727783387188>>> converts a large integer to a byte string, uses the Int.to_bytes () method, and specifies the number of bytes and byte order as follows: >>> x=94522842520747284487117727783387188>>> x.to_bytes (+, ' big ') B ' \x00\x124v\x00x\x90\xab\x00 \xcd\xef\x01\x00#\x004 ' >>> x.to_bytes (+, ' little ') B ' 4\x00#\x00\x01\xef\xcd\x00\xab\x90x\x00v4\x12\x00 ' >>> Use the Int.bit_length () method to determine how many byte bits are required to store this value >>> x=94522842520747284487117727783387188>>> X.bit_length (117)

6. Mathematical operations of complex numbers

Complex numbers can be specified by using Functions complex (real, imag) or floating-point numbers with suffix J

>>> a = complex (2, 4) >>> b= 3-5j>>> a (2+4j) > >> b (3-5j) corresponding to the real, imaginary and conjugate complex >>> a.real2.0>>> a.imag4.0>>>  A.conjugate () (2-4j) All common mathematical operations can work >>> a+b (5-1j) >>> a-b ( -1+9j) >>> a/b ( -0.4117647058823529+0.6470588235294118j) >>> abs (a) 4.47213595499958 performs other complex functions such as sine, cosine, or square root, using the Cmath module >>> import cmath>>> cmath.sin (a) (24.83130584894638-11.356612711218173J) > >> cmath.cos (a) ( -11.36423470640106-24.814651485634183j) >>> cmath.exp (a) (- 4.829809383269385-5.5920560936409816J) The standard mathematical functions of Python do not produce complex values in real cases >>> import math>>>  math.sqrt ( -1) traceback  (most recent call last):  file  "<stdin>" , line 1, in <module>valueerror: math domain error>>>  import cmath>>>&Nbsp;cmath.sqrt ( -1) 1j 

7. Infinity and Nan

Create or test floating-point numbers with positive infinity, negative infinity, or Nan (not a number)

>>> a = float (' inf ') >>> B = float ('-inf ') >>> c = float (' nan ') >>> ainf>>> b-i Nf>>> Cnan using Math.isinf () and Math.isnan () function detection >>> math.isinf (a) true>>> Math.isnan (c) True >>> Math.isinf (b) True infinite number propagates when performing mathematical calculations >>> a+45inf>>> a*10inf>>> 10/ a0.0 Some operations are undefined and return a nan result. >>> a/anan>>> A+bnannan values are propagated across all operations without an exception. >>> c+11nan>>> c/3nan>>> C*3nannan The value of a particular place when the comparison operation between them always returns false. >>> d=float (' nan ') >>> c==dfalse>>> C is dfalse for this reason, testing a nan is worth the only safe way is to use Math.isnan ()

8. Fractional operations

The fractions module can be used to perform mathematical operations that contain fractions.

>>> from fractions import fraction>>> a =fraction (5,4) >>> B = fraction (7, +) >>> AFra Ction (5, 4) >>> bfraction (7) >>> print a+b27/16>>> print a*b35/64 numerator denominator >>> c= a*b& Gt;>> c.numerator35>>> c.denominator64 Convert to decimal >>> float (c) 0.546875 limit denominator >>> c.limit_ Denominator (8) #分母不超过8的最接近的分数Fraction (4, 7) float converted to fractions >>> x=1.75>>> y = fraction (*x.as_integer_ Ratio ()) >>> yfraction (7, 4)

Python Cookbook 2 number Date time (2)