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I want to split a String in python using multiple delimiter. In my case I also want the delimiter which was used returned in a list of delimiters.
Example:
string = '1000+20-12+123-165-564'
(Methods which split the string and return lists with numbers and delimiter)
numbers = ['1000', '20', '12', '123', '165', '564']
delimiter = ['+', '-', '+', '-', '-']
I hope my question is understandable.
You might use re.split for this task following way
import re
string = '1000+20-12+123-165-564'
elements = re.split(r'(\d+)',string) # note capturing group
print(elements) # ['', '1000', '+', '20', '-', '12', '+', '123', '-', '165', '-', '564', '']
numbers = elements[1::2] # last 2 is step, get every 2nd element, start at index 1
delimiter = elements[2::2] # again get every 2nd element, start at index 2
print(numbers) # ['1000', '20', '12', '123', '165', '564']
print(delimiter) # ['+', '-', '+', '-', '-', '']
Just capture (...) the delimiter along with matching/splitting with re.split:
import re
s = '1000+20-12+123-165-564'
parts = re.split(r'([+-])', s)
numbers, delims = parts[::2], parts[1::2]
print(numbers, delims)
['1000', '20', '12', '123', '165', '564'] ['+', '-', '+', '-', '-']
I have a list:
output = ['9', '-', '-', '7', '-', '4', '4', '-', '3', '-', '0', '2']
and I'm trying trying to reduce the '-','-' section to just a single '-', however, haven't had much luck in trying.
final = [output[i] for i in range(len(output)) if output[i] != output[i-1]]
final = 9-7-4-3-02
I've tried that above, but it also reduces the '4','4' to only '4'. So any help would be great.
You should check if the item is equal to the previous item and to '-', which can easily be done in Python using a == b == c.
Note that you should also handle the first character differently, since output[0] == output[0-1] will compare the first item with the last item, which might lead to invalid results.
The following code will handle this:
final = [output[0]] + [output[i] for i in range(1, len(output)) if not (output[i] == output[i-1] == '-')]
The zip() function is your friend for situations where you need to compare/process elements and their predecessor:
final = [a for a,b in zip(output,['']+output) if (a,b) != ('-','-')]
You can use itertools.groupby:
from itertools import groupby as gb
output = ['9', '-', '-', '7', '-', '4', '4', '-', '3', '-', '0', '2']
r = [j for a, b in gb(output) for j in ([a] if a == '-' else b)]
Output:
['9', '-', '7', '-', '4', '4', '-', '3', '-', '0', '2']
I have a lot of python strings such as "A7*4", "Z3+8", "B6 / 11", and I want to split these strings so that they would be in a list, in the format ["A7", "*", "4"], ["B6", "/", "11"], etc. I have used a lot of different split methods but I think I need to just perform the split where there is a math symbol, such as /,*,+,-. I would also need to strip out the whitespace.
Currently I am using the code re.split(r'(\D)', "B6 / 11"), which is returning ['', 'B', '6', ' ', '', '/', '', ' ', '11']. Instead I want to get back ["B6", "/", "11"].
You should split on the character set [+-/*] after removing the whitespace from the string:
>>> import re
>>> def mysplit(mystr):
... return re.split("([+-/*])", mystr.replace(" ", ""))
...
>>> mysplit("A7*4")
['A7', '*', '4']
>>> mysplit("Z3+8")
['Z3', '+', '8']
>>> mysplit("B6 / 11")
['B6', '/', '11']
>>>
There is a way to solve this without regular expressions by using the Python tokenizer. I used a more complex formula to show the capabilities of this solution.
from io import StringIO
import tokenize
formula = "(A7*4) - (Z3+8) - ( B6 / 11)"
print([token[1] for token in tokenize.generate_tokens(StringIO(formula).readline) if token[1]])
Result:
['(', 'A7', '*', '4', ')', '-', '(', 'Z3', '+', '8', ')', '-', '(', 'B6', '/', '11', ')']
If I have a string
'x+13.5*10x-4e1'
how can I split it into the following list of tokens?
['x', '+', '13', '.', '5', '*', '10', 'x', '-', '4', 'e', '1']
Currently I'm using the shlex module:
str = 'x+13.5*10x-4e1'
lexer = shlex.shlex(str)
tokenList = []
for token in lexer:
tokenList.append(str(token))
return tokenList
But this returns:
['x', '+', '13', '.', '5', '*', '10x', '-', '4e1']
So I'm trying to split the letters from the numbers. I'm considering taking the strings that contain both letters and numbers then somehow splitting them, but not sure about how to do this or how to add them all back into the list with the others afterwards. It's important that the tokens stay in order, and I can't have nested lists.
In an ideal world, e and E would not be recognised as letters in the same way, so
'-4e1'
would become
['-', '4e1']
but
'-4x1'
would become
['-', '4', 'x', '1']
Can anybody help?
Use the regular expression module's split() function, to split at
'\d+' -- digits (number characters) and
'\W+' -- non-word characters:
CODE:
import re
print([i for i in re.split(r'(\d+|\W+)', 'x+13.5*10x-4e1') if i])
OUTPUT:
['x', '+', '13', '.', '5', '*', '10', 'x', '-', '4', 'e', '1']
If you don't want to separate the dot (as a floating-point number in the expression) then you should use this:
[\d.]+ -- digit or dot characters (although this allows you to write: 13.5.5
CODE:
print([i for i in re.split(r'([\d.]+|\W+)', 'x+13.5*10x-4e1') if i])
OUTPUT:
['x', '+', '13.5', '*', '10', 'x', '-', '4', 'e', '1']
Another alternative not suggested here, is to using nltk.tokenize module
Well, the problem seems not to be quite simple. I think, a good way to get robust (but, unfortunately, not so short) solution is to use Python Lex-Yacc for creating a full-weight tokenizer. Lex-Yacc is a common (not only Python) practice for this, thus there can exist ready grammars for creating a simple arithmetic tokenizer (like this one), and you have just to fit them to your specific needs.
I have a simple parser written in pyparsing below:
import pyparsing as pp
Token = pp.Word(pp.alphas)("Token")
Modifier = pp.Word(pp.nums)("Modifier")
Random = pp.Group(pp.Keyword("?") + pp.OneOrMore(Modifier))("Random")
Phrase = pp.Group(Token + pp.OneOrMore(Modifier))("Phrase")
Collection = pp.Group(pp.delimitedList(Phrase ^ Random, ","))("Collection")
tree = Collection.parseString("hello 12 2, ? 1 2, word 4, ? 3 4, testing 5")
I then tried doing this:
>>> for name, item in tree[0].items():
print name, item
Phrase ['testing', '5']
Random ['?', '3', '4']
...but for some reason, it returned only the last Phrase and Random items in the tree. How can I get all of them?
(Note: I also tried doing this:
>>> for item in tree[0]:
print item
['hello', '12', '2']
['?', '1', '2']
['word', '4']
['?', '3', '4']
['testing', '5']
...but as you can see, it doesn't return the token name, which I need. I also tried doing item.name, but those always returned empty strings.)
How do I iterate through a pyparsing tree and get every single item, in order, along with the assigned name?
ParseResults can get their defining name by calling getName():
>>> for f in tree[0]: print f.getName(), f.asList()
...
Phrase ['hello', '12', '2']
Random ['?', '1', '2']
Phrase ['word', '4']
Random ['?', '3', '4']
Phrase ['testing', '5']
You can also revert to using setResultsName and setting the listAllMatches argument to True. In version 1.5.6, the expr("name") shortcut was enhanced so that if the name ends with '*', then that is equivalent to expr.setResultsName("name", listAllMatches=True). Here is how the output changes by setting this flag:
>>> Random = pp.Group(pp.Keyword("?") + pp.OneOrMore(Modifier))("Random*")
>>> Phrase = pp.Group(Token + pp.OneOrMore(Modifier))("Phrase*")
>>> Collection = pp.Group(pp.delimitedList(Phrase ^ Random, ","))("Collection")
>>> tree = Collection.parseString("hello 12 2, ? 1 2, word 4, ? 3 4, testing 5")
>>> print tree.dump()
[[['hello', '12', '2'], ['?', '1', '2'], ['word', '4'], ['?', '3', '4'], ['testing', '5']]]
- Collection: [['hello', '12', '2'], ['?', '1', '2'], ['word', '4'], ['?', '3', '4'], ['testing', '5']]
- Phrase: [['hello', '12', '2'], ['word', '4'], ['testing', '5']]
- Random: [['?', '1', '2'], ['?', '3', '4']]