Python学习笔记(6)

Python学习笔记(6)

1）Sequence
Sequence是一对象，一个接一个地保存多种数据项。Python中Sequence有几种不同类型。
下面先看两种Sequence基本类型：字符串和列表
在字符串中访问单个字符：
用for循环迭代字符串，语法如下：
for variable in string:
 statement
 statement
 etc.
例子：
>>> name = 'Juliet'
>>> for ch in name:
 print ch
J
u
l
i
e

例2：
# This program counts the number times
# the letter T appears in a string.
def main():
  count = 0
  my_string = raw_input('Enter a sentence: ')
  for ch in my_string:
  if ch == 'T' or ch == 't':
  count +=1
  print 'The letter T appears',count,'times.'
main()

使用索引访问字符串中的单个字符
字符串的每个字符都有一个序号，表示它在字符串中的位置。
例：
>>> my_string = 'Roses are red'
>>> ch = my_string[6]
>>> ch
'a'
>>> print my_string[0],my_string[6],my_string[10]
R a r

还可以用负数做序号，-1表示字符串最后一个字符，-2表示倒数第2个字符，依次类推。
>>> my_string[-1]
'd'
>>> my_string[-2]
'e'

序号错误
序号有范围，如‘Boston’字符串的序号为0～5以及-1～-6。超出此范围则IndexError。
例：
>>> city='Boston'
>>> print city[6]
Traceback (most recent call last):
  File "<pyshell#11>", line 1, in <module>
  print city[6]
IndexError: string index out of range


字符串分割
格式如下：
string[start:end]
例：
>>> full_name = 'Patty Lynn Smith'
>>> middle_name = full_name[6:10]
>>> print middle_name
Lynn

例：
login.py
# The get_login_name function accepts a first name,
# last name, and ID number as arguments. It returns
# a system login name.
def get_login_name(first,last,idnumber):
  # Get the first three letters of the first name.
  # If the name is less than 3 characters, the
  # slice will return the entire first name.
  set1 = first[0:3]
  # Get the first three letters of the last name.
  # If the name is less than 3 characters, the
  # slice will return the entire last name.
  set2 = last[0:3]
  # Get the last three characters of the student ID.
  # If the ID number is less than 3 characters, the
  # slice will return the entire ID number.
  set3 = idnumber[-3:]
  # Put the sets of characters together.
  login_name = set1+set2+set3
  return login_name

P14.py
import login
def main():
  first = raw_input('Enter your first name: ')
  last = raw_input('Enter your last name: ')
  idnumber = raw_input('Enter your student ID number: ')
  # Get the login name.
  print 'Your system login name is:'
  print login.get_login_name(first, last, idnumber)
main()


测试子串是否在字符串中
用in 或 not in

列表的方法
append(item) 在列表最后添加item
index(item) 返回序号指定的元素
insert(index, item) 在指定序号后插入item
sort() 列表按从小到大的顺序排序
remove(item) 删除列表中第一个出现item的项
reverse() 列表反序
例：
>>> my_list = [1,2,3,4,5]
>>> del my_list[2]
>>> print my_list
[1, 2, 4, 5]

>>> my_list=[5,4,3,123,50,40,30]
>>> print 'The lowest value is',min(my_list)
The lowest value is 3
>>> print 'The highest value is', max(my_list)
The highest value is 123