Searching through a list and replacing items in it...

[Thekid]

Hi, I need to search through a given file and find certain keys and replace them, in this case it's the symbol "%". I'm not sure how to go about this.

f = open("numbers.txt","r")
contents = f.read( )
# I'm not sure why the .split is in here but someone suggested it to me so I 
# included it. I could .split("%") but then what?
fields = contents.split(",")
print fields
 

# numbers.txt=
1234435%357435734763736%474526435151463267%2394324 9023403478234724234782347234234247824273423478235% 4728340723840%472347234023742%72304372104%472389%4 7204
47242%7420472394729472472390427472482%742947247289 04273%34%
21211212122121%1121212121%67676767676767%878787878 78787%

I can print the file out like this but I need to replace the 1st, 5th & 13th "%" with "$".

I tried to do something like this to see if it would just find "%" but it didn't work:

f = open("numbers.txt","r")
contents = f.read( )
data = contents.split(",")
if data.find("%"):
print "Symbol found"
 

^ gets error message because the .split puts it into a list. I also tried re.search("%").

Any suggestions?

[bvdet]

Hi, I need to search through a given file and find certain keys and replace them, in this case it's the symbol "%". I'm not sure how to go about this.

f = open("numbers.txt","r")
contents = f.read( )
# I'm not sure why the .split is in here but someone suggested it to me so I 
# included it. I could .split("%") but then what?
fields = contents.split(",")
print fields
 

# numbers.txt=
1234435%357435734763736%474526435151463267%2394324 9023403478234724234782347234234247824273423478235% 4728340723840%472347234023742%72304372104%472389%4 7204
47242%7420472394729472472390427472482%742947247289 04273%34%
21211212122121%1121212121%67676767676767%878787878 78787%

I can print the file out like this but I need to replace the 1st, 5th & 13th "%" with "$".

I tried to do something like this to see if it would just find "%" but it didn't work:

f = open("numbers.txt","r")
contents = f.read( )
data = contents.split(",")
if data.find("%"):
print "Symbol found"
 

^ gets error message because the .split puts it into a list. I also tried re.search("%").

Any suggestions?

String methods can be used to accomplish your task.

def replace_pos(s, old, new, posList):
    idx = -1
    count = 0
    while True:
        '''
        s.find() returns the position of the substring.
        When the end of string is reached and no more
        occurrances of substring are found, s.find()
        returns -1.
        '''
        idx = s.find(old, idx+1)
        count += 1
        if idx == -1:
            return s
        elif count in posList:
            s = '%s%s%s' % (s[:idx],new,s[(idx+len(old)):])   
 
fn = r'H:\TEMP\temsys\numbers1.txt'
s = open(fn).read()
oldStr = '%'
newStr = '$'
posList = [1,5,13]
s1 = replace_pos(s, oldStr, newStr, posList)

There is no need to split the string into a list, although there is a way to get the same result.

[Thekid]

Great, thank you that works. Now what if I need to change all of them instead of just a few, but don't know how many are in the file? How can I replace them all?

[bvdet]

Great, thank you that works. Now what if I need to change all of them instead of just a few, but don't know how many are in the file? How can I replace them all?

That's much easier.

s2 = s.replace('%', '$')

[Thekid]

Once again thanks, that does the trick. One last question regarding this, what about a loop that will go through and try various combinations? For example, let's say it will replace positions 1,2,3 then try 1,2,4, then try 1,2,5 etc....

[bvdet]

Once again thanks, that does the trick. One last question regarding this, what about a loop that will go through and try various combinations? For example, let's say it will replace positions 1,2,3 then try 1,2,4, then try 1,2,5 etc....

The function replace_pos() should work for that.

[Thekid]

The function replace_pos() should work for that.

I've played around with the replace_pos() but still can't seem to get it to work as a loop. This is it so far:

def replace_pos(s, old, new, posList):
    idx = -1
    count = 0
    while True:
        '''
        s.find() returns the position of the substring.
        When the end of string is reached and no more
        occurrances of substring are found, s.find()
        returns -1.
        '''
        idx = s.find(old, idx+1)
        count += 1
        if idx == -1:
            return s
        elif count in posList:
            s = '%s%s%s' % (s[:idx],new,s[(idx+len(old)):])   
 
# I changed this part slightly
fn = open("numbers.txt","r")
s = (fn).read()
oldStr = "#"
newStr = "@"
posList = [1,2,3]
s1 = s.replace("%","#")
s2 = replace_pos(s1, oldStr, newStr, posList)
print s2
 
 

This is taking the 'numbers.txt' and first replacing all of the '%' symbols with '#'. It then replaces the 1,2,3 '#' symbols with '@'. What I want to do is first change all of the symbols but then have a loop replace the 1,2,3 symbols. If they are the correct combinations then it's done, if not I need the code to replace the 1,2,4 positions, then 1,2,5 and so on until all combinations are checked. Also, I can 'write' to the file by adding the code below but it doesn't fit in to the loop because it saves the changes and that throws off the next run through of the code:

 
solution = s2
f 2= open("numbers.txt","w")
f2.write(solution)
f2.close
print solution
 

[bvdet]

I've played around with the replace_pos() but still can't seem to get it to work as a loop. This is it so far:

def replace_pos(s, old, new, posList):
    idx = -1
    count = 0
    while True:
        '''
        s.find() returns the position of the substring.
        When the end of string is reached and no more
        occurrances of substring are found, s.find()
        returns -1.
        '''
        idx = s.find(old, idx+1)
        count += 1
        if idx == -1:
            return s
        elif count in posList:
            s = '%s%s%s' % (s[:idx],new,s[(idx+len(old)):])   
 
# I changed this part slightly
fn = open("numbers.txt","r")
s = (fn).read()
oldStr = "#"
newStr = "@"
posList = [1,2,3]
s1 = s.replace("%","#")
s2 = replace_pos(s1, oldStr, newStr, posList)
print s2
 
 

This is taking the 'numbers.txt' and first replacing all of the '%' symbols with '#'. It then replaces the 1,2,3 '#' symbols with '@'. What I want to do is first change all of the symbols but then have a loop replace the 1,2,3 symbols. If they are the correct combinations then it's done, if not I need the code to replace the 1,2,4 positions, then 1,2,5 and so on until all combinations are checked. Also, I can 'write' to the file by adding the code below but it doesn't fit in to the loop because it saves the changes and that throws off the next run through of the code:

 
solution = s2
f 2= open("numbers.txt","w")
f2.write(solution)
f2.close
print solution
 

You need to have some way to determine the replacement position lists. What are "all combinations"? After you create the all combinations list, then you can iterate on that list.

comb_list = [[1,2,3], [1,2,4], [1,2,5], [1,3,4], [1,4,5], [2,3,4], [3,4,5]]
 
for clist in comb_list:
    s1 = replace_pos(s, oldStr, newStr, clist)