How can I get the position of a character inside a string in Python?
bad_coder
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asked Feb 19, 2010 at 6:32
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There are two string methods for this, find() and index(). The difference between the two is what happens when the search string isn't found. find() returns -1 and index() raises a ValueError.
Using find()
>>> myString = 'Position of a character' >>> myString.find('s') 2 >>> myString.find('x') -1Using index()
>>> myString = 'Position of a character' >>> myString.index('s') 2 >>> myString.index('x') Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: substring not foundFrom the Python manual
string.find(s, sub[, start[, end]])
Return the lowest index in s where the substring sub is found such that sub is wholly contained in s[start:end]. Return -1 on failure. Defaults for start and end and interpretation of negative values is the same as for slices.
And:
string.index(s, sub[, start[, end]])
Like find() but raise ValueError when the substring is not found.
Tomerikoo
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answered Feb 19, 2010 at 6:35
Eli BenderskyEli Bendersky
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Just for a sake of completeness, if you need to find all positions of a character in a string, you can do the following:
s = 'shak#spea#e' c = '#' print([pos for pos, char in enumerate(s) if char == c])which will print: [4, 9]
Jolbas
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answered Sep 26, 2015 at 7:59
Salvador DaliSalvador Dali
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>>> s="mystring" >>> s.index("r") 4 >>> s.find("r") 4
"Long winded" way
>>> for i,c in enumerate(s): ... if "r"==c: print i ... 4to get substring,
>>> s="mystring" >>> s[4:10] 'ring'answered Feb 19, 2010 at 6:36
ghostdog74ghostdog74
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Just for completion, in the case I want to find the extension in a file name in order to check it, I need to find the last '.', in this case use rfind:
path = 'toto.titi.tata..xls' path.find('.') 4 path.rfind('.') 15in my case, I use the following, which works whatever the complete file name is:
filename_without_extension = complete_name[:complete_name.rfind('.')]answered Sep 28, 2017 at 6:37
A.JolyA.Joly
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What happens when the string contains a duplicate character? from my experience with index() I saw that for duplicate you get back the same index.
For example:
s = 'abccde' for c in s: print('%s, %d' % (c, s.index(c)))would return:
a, 0 b, 1 c, 2 c, 2 d, 4In that case you can do something like that:
for i, character in enumerate(my_string): # i is the position of the character in the string
answered Jul 1, 2015 at 12:40
DimSarakDimSarak
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string.find(character) string.index(character)
Perhaps you'd like to have a look at the documentation to find out what the difference between the two is.
Brad Koch
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answered Feb 19, 2010 at 6:37
John MachinJohn Machin
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A character might appear multiple times in a string. For example in a string sentence, position of e is 1, 4, 7 (because indexing usually starts from zero). but what I find is both of the functions find() and index() returns first position of a character. So, this can be solved doing this:
def charposition(string, char): pos = [] #list to store positions for each 'char' in 'string' for n in range(len(string)): if string[n] == char: pos.append(n) return pos s = "sentence" print(charposition(s, 'e')) #Output: [1, 4, 7]answered Sep 16, 2018 at 9:33
itssubasitssubas
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If you want to find the first match.
Python has a in-built string method that does the work: index().
string.index(value, start, end)Where:
- Value: (Required) The value to search for.
- start: (Optional) Where to start the search. Default is 0.
- end: (Optional) Where to end the search. Default is to the end of the string.
If you want to find all the matches.
Let's say you need all the indexes where the character match is and not just the first one.
The pythonic way would be to use enumerate().
def character_indexes(): string = "Hello World! This is an example sentence with no meaning." match = "i" indexes_of_match = [] for index, character in enumerate(string): if character == match: indexes_of_match.append(index) return indexes_of_match print(character_indexes()) # [15, 18, 42, 53]Or even better with a list comprehension:
def character_indexes_comprehension(): string = "Hello World! This is an example sentence with no meaning." match = "i" return [index for index, character in enumerate(string) if character == match] print(character_indexes_comprehension()) # [15, 18, 42, 53]answered Jan 26, 2021 at 5:01
Guzman OjeroGuzman Ojero
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more_itertools.locate is a third-party tool that finds all indicies of items that satisfy a condition.
Here we find all index locations of the letter "i".
Given
import more_itertools as mit text = "supercalifragilisticexpialidocious" search = lambda x: x == "i"Code
list(mit.locate(text, search)) # [8, 13, 15, 18, 23, 26, 30]answered Feb 9, 2018 at 0:46
pylangpylang
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A solution with numpy for quick access to all indexes:
string_array = np.array(list(my_string)) char_indexes = np.where(string_array == 'C')answered Jan 15, 2020 at 20:40
SebSeb
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Most methods I found refer to finding the first substring in a string. To find all the substrings, you need to work around.
For example:
Define the string
vars = 'iloveyoutosimidaandilikeyou'
Define the substring
key = 'you'Define a function that can find the location for all the substrings within the string
def find_all_loc(vars, key): pos = [] start = 0 end = len(vars) while True: loc = vars.find(key, start, end) if loc is -1: break else: pos.append(loc) start = loc + len(key) return pos pos = find_all_loc(vars, key) print(pos) [5, 24]
Emi OB
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answered Nov 5, 2021 at 8:44