Python 学习入门（18）—— 字符串

Python判断字符串只包含数字

一种方法是 a.isdigit()，但这种方法对于包含正负号的数字字符串无效，更为准确的为：

#!/usr/bin/python
# -*- coding:utf-8 -*-
#
# http://blog.ithomer.net

import sys
import math

# 判断是否为数字
def isNum(value):
    try:
        value + 1
    except TypeError:
        return False
    else:
        return True

# 判断是否为数字
def isNum2(value):
    try:
        x = int(value)
    except TypeError:
        return False
    except ValueError:
        return False
    except Exception, e:
        return False
    else:
        return True


def test1():
    
    a = "123abcDE"
    print a.isalnum()       # True, 所有字符都是数字或者字母

    a = "abcDE"
    print a.isalpha()       # True, 所有字符都是字母

    a = "123.3"
    print a.isdigit()       # False, 所有字符都是数字

    a = "abcde"
    print a.islower()       # True, 所有字符都是小写

    a = "ABCDE"
    print a.isupper()       # True, 所有字符都是大写

    a = "Abcde"
    print a.istitle()       # True, 所有单词都是首字母大写，像标题

    a = "\t"
    print a.isspace()       # True, 所有字符都是空白字符、\t、\n、\r

    arr = (1, 2.1, -3, -4.5, '123a', 'abc', 'aBC', 'Abc', 'ABC', '\t')
    for a in arr:
        print a,isNum(a)

    '''
    1 True
    2.1 True
    -3 True
    -4.5 True
    123a False
    abc False
    aBC False
    Abc False
    ABC False
        False
    '''

    for a in arr:
        print a,isNum2(a)
    '''
    1 True
    2.1 True
    -3 True
    -4.5 True
    123a False
    abc False
    aBC False
    Abc False
    ABC False
        False
    '''

这样更准确一些，适用性也更广。但如果你已经确信没有正负号，使用字符串的isdigit()方法则更为方便。

Python 字符串操作，如string替换、删除、截取、复制、连接、比较、查找、包含、大小写转换、分割等

def test2():

    # 复制字符串 
    str1 = "ithomer.net"
    str2 = str1
    str1 = "blog"
    print str1, str2        # blog ithomer.net

    # 连接字符串
    str1 = "ithomer.net"
    str2 = "blog."
    str2 += str1
    print str1, str2        # ithomer.net blog.ithomer.net
    
    # 查找字符
    str1 = "ithomer.net"
    str2 = ".net"
    pos = str1.index(str2)
    print pos               # 7

    # 比较字符串
    str1 = "blog.ithomer.net"
    str2 = "forum.ithomer.net"
    pos = cmp(str1, str2)
    print pos               # -1

    # 是否包含指定的字符
    str1 = "blog.ithomer.net"
    str2 = ".ithomer."
    pos = len(str1 and str2)
    print pos               # 9

    # 字符串长度
    str1 = "blog.ithomer.net"
    pos = len(str1)
    print pos               # 16

    # 字符串大小写转换
    str1 = "blog.ithomer.net"
    str2 = "BLOG.ithomer.NET"
    print str1.upper()      # BLOG.ITHOMER.NET
    print str2.lower()      # blog.ithomer.net

    # 追加指定长度的字符串
    str1 = "blog.ithomer.net"
    str2 = "1234567"
    n = 3
    str1 += str2[0:n]
    print str1,str2         # blog.ithomer.net123 1234567

    # 字符串指定长度比较
    str1 = "blog.ithomer.net"
    str2 = "blog.ithomer.NET"
    n = 11
    print cmp(str1[0:n], str2[0:n])     # 0

    # 复制指定长度的字符
    str1 = "blog.ithomer.net"
    str2 = ""
    n = 12
    print str1[0:n]         # blog.ithomer

    # 将字符串前n个字符替换为指定的字符
    str1 = "blog.ithomer.net"
    ch = 'r'
    n = 3
    print n*ch + str1       # rrrblog.ithomer.net

    # 扫描字符串 
    sStr = 'cekjgdklab'   
    sStr1 = 'gka'   
    nPos = -1 
    for c in sStr1: 
        print c
    print nPos   

    # 翻转字符串 
    str1 = "ithomer.net"
    str2 = str1[::-1]
    print str1,str2         # ithomer.net ten.remohti

    # 查找字符串
    str1 = "ithomer.net"
    str2 = ".net"
    pos = str1.find(str2)
    print pos               # 7
    
    # 分割字符串
    str1 = "blog.ithomer.net"
    str2 = "."
    str3 = str1[str1.find(str2) + 1:]
    print str3              # ithomer.net
    print str1.split(str2)  # ['blog', 'ithomer', 'net']

    # 连接字符串
    str1 = ['blog', 'ithomer', 'net']
    str2 = "."
    str3 = str2.join(str1)
    print str3              # blog.ithomer.net

    # 只显示字母与数字
    str1 = "521.ithomer.NET $ @ # ! 1314"
    fmt = "abcdefghijklmnopqrstuvwxyz0123456789"
    for c in str1:
        if not c in fmt:
            str1 = str1.replace(c,'')
    print str1              # 521ithomer1314

参考推荐：

Python字符串操作

Python difflib