CODEWITHSUNDEEP
python
Pargrammisa
Pargrammisa

Reputation: 73

searching string to find indexes

I want to find all indexes of "a" item of my string, but it prints only the first one. What is the problem of this program:

def str_lookup_reverse(s, c):
    for index in range(len(s)-1):
        if s[index] == c:
            print(index)

s = "parisa"
str_lookup_reverse(s, "a")

Upvotes: 2

Views: 66

Answers (7)

RoadRunner
RoadRunner

Reputation: 26315

Very close. Your loop is ending too soon, you need to do loop over the indices of the whole string:

for index in range(len(s))

instead of:

for index in range(len(s)-1)

which loops over everything but the last character, where your second "a" occurs. This means that your second "a" never gets reached.

Additionally, a more pythonic way is to use enumerate():

def str_lookup_reverse(s, c):
    for i, e in enumerate(s):
        if e == c:
            print(i)

s = "parisa"
str_lookup_reverse(s, "a")

Which also outputs what you want:

 1
 5

Upvotes: 1

Poiz
Poiz

Reputation: 7617

You could capture the index by wrapping the String(s) with enumerate() as shown below. 

def str_lookup_reverse(s, c):
    index_list  = []
    for index, char in enumerate(s):
        if char == c:
            index_list.append(index)
            # print(index)
    return index_list


s           = "parisa"
index_list  = str_lookup_reverse(s, "a") 
print(index_list)        ## PRINTS: [1, 5]

Upvotes: 1

Ankush Rathi
Ankush Rathi

Reputation: 620

You can also just go through the characters like this - 

def str_lookup_reverse(s, c):
    ind = 0
    for eachChar in s:
       ind += 1 
          if eachChar == c:
          print(ind)

s = "parisa" 
str_lookup_reverse(s, "a")

Upvotes: 0

fugu
fugu

Reputation: 6578

You are using len(s)-1, which will not iterate over the full length of the string. You should use len(s):

def str_lookup_reverse(s, c):
    for index in range(len(s)):
        if s[index] == c:
            print(index)

s = "parisa"
str_lookup_reverse(s, "a")

To illustrate the problem, compare: 

text='parisa'
for i in range(len(text)-1):
    print("%s, %s") % (i, text[i])

0, p
1, a
2, r
3, i
4, s

With:

for i in range(len(text)):
    print("%s, %s") % (i, text[i])

0, p
1, a
2, r
3, i
4, s
5, a

Upvotes: 2

zipa
zipa

Reputation: 27879

Have you tried it like this:

for i, letter in enumerate(s):
    if letter == c:
        print(i)

Upvotes: 4

heemayl
heemayl

Reputation: 42047

As others have mentioned your issue with for index in range(len(s)-1):, which needs to be for index in range(len(s)):.

Now, here's an approach with enumerate:

[i for(i, v) in enumerate(s) if v == 'a']

e.g.

In [54]: s = "parisa"

In [55]: [i for(i, v) in enumerate(s) if v == 'a']
Out[55]: [1, 5]

As a function:

def findidx(string, char):
    return [i for(i, v) in enumerate(string) if v == char]

e.g.

In [56]: def findidx(string, char):
   ....:     return [i for(i, v) in enumerate(string) if v == char]
   ....: 

In [57]: findidx(s, "a")
Out[57]: [1, 5]

Upvotes: 1

Jack Nicholson
Jack Nicholson

Reputation: 205

You're removing the length of the string... So you're removing the last a making s = 'paris'

def str_lookup_reverse(s, c):
    for index in range(len(s)-1):
        if s[index] == c:
            print(index)

s = "parisa"
str_lookup_reverse(s, "a")

This will solve your problem:

def str_lookup_reverse(s, c):
    for index in range(len(s)):
        if s[index] == c:
            print(index)

s = "parisa"
str_lookup_reverse(s, "a")

Upvotes: 2

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