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