Python 基础语法知识(一)

Python 随版本的不同,语法也有一些差异。 具体可以参考最新的Python帮助文档。 以下说明都是基于Python 3.1 版本。 

  一. Python 变量类型
  #整型
  integer_number = 90

  #浮点
  float_number = 90.4

  #复数
  complex_number = 10 + 10j

  #list 序列:列表、元组和字符串都是序列,序列的两个主要特点是索引操作符和切片操作符。

  sample_list = [1,2,3,'abc']

  #dictionary 字典
  sample_dic = {"key":value, 2:3}

  #tuple 只读的序列
  sample_tuple = (1,3,"ab")


  二. Python 程序流程控制
  2.1 条件判断结构
  flag1 = some_value
  flag2 = other_value
  if flag1:
  do_function_1()
  elif flag2:
  do_function_2()
  else:
  do_function_3()

  2.2 循环结构
  for i in range(0, 10):
  print(i)

  for i in ['a','b','c','dd','eee'];
  print(i)

  三. Print 函数及格式化输出
  3.1 Print 自动换行
  在Python 3.0 以后,Python 在print 函数上做了修改。 在Python 2.x 版本中,示例如下:
  for i in range(0,5):
  print i
  默认情况是自动换行的,如果说是不自动换行,在最后加逗号就可以了:print i,

  在Python 3.0 的文档里,对print 说明如下:
   print([object, ...], *, sep=' ', end='\n', file=sys.stdout) 
  Print object(s) to the stream file, separated by sep and followed by end. sep, end and file, if present, must be given as keyword arguments.
  All non-keyword arguments are converted to strings like str() does and written to the stream, separated by sep and followed by end. Both sep and end must be strings; they can also be None, which means to use the default values. If no object is given, print() will just write end.
  The file argument must be an object with a write(string) method; if it is not present or None, sys.stdout will be used.

  在Python 3.x 版本中,如果不想自动换行,就需要使用end 参数。该参数默认使用'\n',即回车换行,如果不想使用,换成其他字符,或者为空即可。 示例如下:

  >>> for i in range(5):
  print(i,end='')

  01234
  >>> for i in range(5):
  print(i)

  0
  1
  2
  3
  4
  >>> for i in range(5):
  print(i,end=',')

  0,1,2,3,4,



  3.2 print 正常输出
  使用print输出各型的 
  (1). 字符串
  (2). 整数
  (3). 浮点数
  (4). 出度及精度控制
  >>> str = 'tianlesoftware oracle dba'
  >>> print(str);
  tianlesoftware oracle dba
  >>> 
  3.3 格式化输出整数
  python print也支持参数格式化,与C言的printf似, 示例:

  >>> str = "the length of (%s) is %d" %('Hello World',len('Hello World'))
  >>> print(str)
  the length of (Hello World) is 11

  或者直接写道print里:
  >>> print( "the length of (%s) is %d" %('Hello World',len('Hello World')))
  the length of (Hello World) is 11
  >>> 

  3.4 格式化输出16制整数
  nHex = 0x20
  #%x --- hex 十六进制
  #%d --- dec 十进制
  #%o --- oct 八进制

  示例:
  >>> nHex = 0x20
  >>> print("nHex = %x,nDec = %d,nOct = %o" %(nHex,nHex,nHex))
  nHex = 20,nDec = 32,nOct = 40

  3.5 格式化输出浮点数(float)
  #导入math 模块
  >>> import math
  #default
  >>> print("PI = %f" % math.pi)
  PI = 3.141593
  #width = 10,precise = 3,align = left
  >>> print("PI = %10.3f" % math.pi)
  PI = 3.142
  #width = 10,precise = 3,align = rigth
  >>> print("PI = %-10.3f" % math.pi)
  PI = 3.142 
  #前面填充字符
  >>> print("PI = %06d" % int(math.pi))
  PI = 000003
  >>> 

  3.6 格式化输出字符串(string)
  # precise = 3
  >>> print("%.3s " % ("jcodeer"))

  jco
  #precise = 4
  >>> print("%.*s" % (4,"jcodeer"))
  jcod
  # width = 10,precise = 3
  >>> print ("%10.3s" % ("jcodeer"))

  jco

  3.7 输出列表(list)
  #list直接打印即可
  >>> l = [1,2,3,4,'tianlesoftware']
  >>> print(l)
  [1, 2, 3, 4, 'tianlesoftware']
  >>> print(l[0])
  1
  >>> print(l[4])
  tianlesoftware

  3.8 输出字典(dictionary)
  >>> dave = {1:'A',2:'B',3:'C',4:'D'}
  >>> print(dave)
  {1: 'A', 2: 'B', 3: 'C', 4: 'D'}
  >>> print(dave[4])
  D
  >>> print(dave[1])
  A

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转载自blog.csdn.net/ugly_girl/article/details/80534098