python中字符串比较使用is、==和cmp()总结

The operators ``is`` and ``is not`` test for object identity: ``x is
y`` is true if and only if *x* and *y* are the same object. ``x is
not y`` yields the inverse truth value.
 
cmp(...)
 cmp(x, y) -> integer
 
 Return negative if x<y, zero if x==y, positive if x>y.

> a = 256
> b = 256
> id(a)
9987148
> id(b)
9987148
> a = 257
> b = 257
> id(a)
11662816
> id(b)
11662828

#!/usr/bin/python
 
strtmp = '192.169.1.161'
file_object = open(r'public_ip.txt')
try:
 all_the_text = file_object.readlines()
 firstline = all_the_text[0].rstrip()
finally:
 file_object.close()
 
#print firstline
 
#if strtmp == firstline:
s = (strtmp is firstline)
print s
if (strtmp is firstline):
 print 'yes'
else:
 print 'no'

#-*-conding:utf-8-*-
i='xinwen';
m=input();
if i==m:
 print('yes');
else:
 print('no');
 
input();

#!/usr/bin/python
# Filename: if.py
 
number = 23
guess = int(raw_input('Enter an integer : '))
 
if guess == number:
 print 'Congratulations, you guessed it.' # New block starts here
 print "(but you do not win any prizes!)" # New block ends here
elif guess < number:
 print 'No, it is a little higher than that' # Another block
 # You can do whatever you want in a block ...
else:
 print 'No, it is a little lower than that'
 # you must have guess > number to reach here
 
print 'Done'
# This last statement is always executed, after the if statement is executed

> x='a'
> x+'b' is 'ab'
False
> x+'b' == 'ab'
True
> cmp(x+'b','ab')
0
> id(x+'b')
32468384L
> id('ab')
46933696L
>

> a='abc'
> b='abc'
> a is b
True
> id(a) == id(b)
True
>