How to subtract two strings?

问题

I have a long string, which is basically a list like str="lamp, bag, mirror," (and other items)

I was wondering if I can add or subtract some items, in other programming languages I can easily do: str=str-"bag," and get str="lamp, mirror," this doesnt work in python (I'm using 2.7 on a W8 pc)

Is there a way to split the string across say "bag," and somehow use that as a subtraction? Then I still need to figure out how to add.

回答1:

you could also just do

print "lamp, bag, mirror".replace("bag,","")

回答2:

How about this?:

def substract(a, b):                              
    return "".join(a.rsplit(b))

回答3:

You can do this as long as you use well-formed lists:

s0 = "lamp, bag, mirror"
s = s0.split(", ") # s is a list: ["lamp", "bag", "mirror"]

If the list is not well-formed, you can do as follows, as suggested by @Lattyware:

s = [item.strip() for item in s0.split(',')]

Now to delete the element:

s.remove("bag")
s
=> ["lamp", "mirror"]

Either way - to reconstruct the string, use join():

", ".join(s)
=> "lamp, mirror"

A different approach would be to use replace() - but be careful with the string you want to replace, for example "mirror" doesn't have a trailing , at the end.

s0 = "lamp, bag, mirror"
s0.replace("bag, ", "")
=> "lamp, mirror"

回答4:

you should convert your string to a list of string then do what you want. look

my_list="lamp, bag, mirror".split(',')
my_list.remove('bag')
my_str = ",".join(my_list)

回答5:

If you have two strings like below:

t1 = 'how are you'
t2 = 'How is he'

and you want to subtract these two strings then you can use the below code:

l1 = t1.lower().split()
l2 = t2.lower().split()
s1 = ""
s2 = ""
for i in l1:
  if i not in l2:
    s1 = s1 + " " + i 
for j in l2:
  if j not in l1:
    s2 = s2 + " " + j 

new = s1 + " " + s2
print new

Output will be like:

are you is he

回答6:

from re import sub

def Str2MinusStr1 (str1, str2, n=1) :
    return sub(r'%s' % (str2), '', str1, n)

Str2MinusStr1 ('aabbaa', 'a')  
# result 'abbaa'

Str2MinusStr1 ('aabbaa', 'ab')  
# result 'abaa'

Str2MinusStr1 ('aabbaa', 'a', 0)  
# result 'bb'

# n = number of occurences. 
# 0 means all, else means n of occurences. 
# str2 can be any regular expression.

回答7:

Using regular expression example:

import re

text = "lamp, bag, mirror"
word = "bag"

pattern = re.compile("[^\w]+")
result = pattern.split(text)
result.remove(word)
print ", ".join(result)

回答8:

Using the following you can add more words to remove (["bag", "mirror", ...])

(s0, to_remove) = ("lamp, bag, mirror", ["bag"])
s0 = ", ".join([x for x in s0.split(", ") if x not in to_remove])
=> "lamp, mirror"

来源：https://stackoverflow.com/questions/18454570/how-to-subtract-two-strings

标签

python

string

addition

subtraction