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How do I concatenate a list of strings into a single string?
For example, given ['this', 'is', 'a', 'sentence'], how do I get "this-is-a-sentence"?
For handling a few strings in separate variables, see How do I append one string to another in Python?.
For the opposite process - creating a list from a string - see How do I split a string into a list of characters? or How do I split a string into a list of words? as appropriate.
Use str.join:
>>> words = ['this', 'is', 'a', 'sentence']
>>> '-'.join(words)
'this-is-a-sentence'
>>> ' '.join(words)
'this is a sentence'
A more generic way (covering also lists of numbers) to convert a list to a string would be:
>>> my_lst = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> my_lst_str = ''.join(map(str, my_lst))
>>> print(my_lst_str)
12345678910
It's very useful for beginners to know
why join is a string method.
It's very strange at the beginning, but very useful after this.
The result of join is always a string, but the object to be joined can be of many types (generators, list, tuples, etc).
.join is faster because it allocates memory only once. Better than classical concatenation (see, extended explanation).
Once you learn it, it's very comfortable and you can do tricks like this to add parentheses.
>>> ",".join("12345").join(("(",")"))
Out:
'(1,2,3,4,5)'
>>> list = ["(",")"]
>>> ",".join("12345").join(list)
Out:
'(1,2,3,4,5)'
Edit from the future: Please don't use the answer below. This function was removed in Python 3 and Python 2 is dead. Even if you are still using Python 2 you should write Python 3 ready code to make the inevitable upgrade easier.
Although #Burhan Khalid's answer is good, I think it's more understandable like this:
from str import join
sentence = ['this','is','a','sentence']
join(sentence, "-")
The second argument to join() is optional and defaults to " ".
list_abc = ['aaa', 'bbb', 'ccc']
string = ''.join(list_abc)
print(string)
>>> aaabbbccc
string = ','.join(list_abc)
print(string)
>>> aaa,bbb,ccc
string = '-'.join(list_abc)
print(string)
>>> aaa-bbb-ccc
string = '\n'.join(list_abc)
print(string)
>>> aaa
>>> bbb
>>> ccc
We can also use Python's reduce function:
from functools import reduce
sentence = ['this','is','a','sentence']
out_str = str(reduce(lambda x,y: x+"-"+y, sentence))
print(out_str)
We can specify how we join the string. Instead of '-', we can use ' ':
sentence = ['this','is','a','sentence']
s=(" ".join(sentence))
print(s)
If you have a mixed content list and want to stringify it, here is one way:
Consider this list:
>>> aa
[None, 10, 'hello']
Convert it to string:
>>> st = ', '.join(map(str, map(lambda x: f'"{x}"' if isinstance(x, str) else x, aa)))
>>> st = '[' + st + ']'
>>> st
'[None, 10, "hello"]'
If required, convert back to the list:
>>> ast.literal_eval(st)
[None, 10, 'hello']
If you want to generate a string of strings separated by commas in final result, you can use something like this:
sentence = ['this','is','a','sentence']
sentences_strings = "'" + "','".join(sentence) + "'"
print (sentences_strings) # you will get "'this','is','a','sentence'"
def eggs(someParameter):
del spam[3]
someParameter.insert(3, ' and cats.')
spam = ['apples', 'bananas', 'tofu', 'cats']
eggs(spam)
spam =(','.join(spam))
print(spam)
Without .join() method you can use this method:
my_list=["this","is","a","sentence"]
concenated_string=""
for string in range(len(my_list)):
if string == len(my_list)-1:
concenated_string+=my_list[string]
else:
concenated_string+=f'{my_list[string]}-'
print([concenated_string])
>>> ['this-is-a-sentence']
So, range based for loop in this example , when the python reach the last word of your list, it should'nt add "-" to your concenated_string. If its not last word of your string always append "-" string to your concenated_string variable.
myArray = []
textFile = open("file.txt")
lines = textFile.readlines()
for line in lines:
myArray.append(line.split(" "))
print (myArray)
This code outputs
[['a\n'], ['b\n'], ['c\n'], ['d']]
What would I need to do to make it output
a, b, c, d
You're adding a list to your result (split returns a list). Moreover, specifying "space" for split character isn't the best choice, because it doesn't remove linefeed, carriage return, double spaces which create an empty element.
You could do this using a list comprehension, splitting the items without argument (so the \n naturally goes away)
with open("file.txt") as lines:
myArray = [x for line in lines for x in line.split()]
(note the with block so file is closed as soon as exited, and the double loop to "flatten" the list of lists into a single list: can handle more than 1 element in a line)
then, either you print the representation of the array
print (myArray)
to get:
['a', 'b', 'c', 'd']
or you generate a joined string using comma+space
print(", ".join(myArray))
result:
a, b, c, d
You could do the following:
myArray = [[v.strip() for v in x] for x in myArray]
This will remove all the formatting characters.
If you do not want each character to be in its own array, you could then do:
myArray = [v[0] for v in myArray]
To print, then 'print(', '.join(myArray))
It seems you should be using strip() (trim whitespace) rather than split() (which generates a list of chunks of string.
myArray.append(line.strip())
Then 'print(myArray)' will generate:
['a', 'b', 'c', 'd']
To print 'a, b, c, d' you can use join():
print(', '.join(myArray))
You can try something like:
import re
arr = [['a\n'], ['b\n'], ['c\n'], ['d']]
arr = ( ", ".join( repr(e) for e in arr ))
arr = arr.replace('\\n', '')
new = re.sub(r'[^a-zA-Z0-9,]+', '', arr)
print(new)
Result:
a,b,c,d
I am trying to use line.strip() and line.split() to get an element out of a file, but this always gives me a list of string, does line.split() always return a string? how can I just get a list of elements instead of a list of 'elements'?
myfile = open('myfile.txt','r')
for line in myfile:
line_strip = line.strip()
myline = line_strip.split(' ')
print(myline)
So my code gives me ['hello','hi']
I want to get a list out of the file look likes[hello,hi]
[2.856,9.678,6.001] 6 Mary
[8.923,3.125,0.588] 7 Louis
[7.122,9.023,4,421] 16 Ariel
so when I try
list = []
list.append((mylist[0][0],mylist[0][1]))
I actually want a list = [(2.856,9.678),(8.923,3.123),(7.122,9.023)]
but it seems this mylist[0][0] refers to '[' in my file
my_string = 'hello'
my_list = list(my_string) # ['h', 'e', 'l', 'l', 'o']
my_new_string = ''.join(my_list) # 'hello'
I think you are looking for this
>>> print("[{}]".format(", ".join(data)))
[1, 2, 3]
To address your question, though
this always gives me a list of string,
Right. As str.split() should do.
does line.split() always return a string?
Assuming type(line) == str, then no, it returns a list of string elements from the split line.
how can I just get a list of elements instead of a list of 'elements'?
Your "elements" are strings. The ' marks are only Python's repr of a str type.
For example...
print('4') # 4
print(repr('4')) # '4'
line = "1,2,3"
data = line.split(",")
print(data) # ['1', '2', '3']
You can cast to a different data-type as you wish
print([float(x) for x in data]) # [1.0, 2.0, 3.0]
For what you posted, use a regex:
>>> s="[2.856,9.678,6.001] 6 Mary"
>>> import re
>>> [float(e) for e in re.search(r'\[([^\]]+)',s).group(1).split(',')]
[2.856, 9.678, 6.001]
For all the lines you posted (and this would be similar to a file) you might do:
>>> txt="""\
... [2.856,9.678,6.001] 6 Mary
... [8.923,3.125,0.588] 7 Louis
... [7.122,9.023,4,421] 16 Ariel"""
>>> for line in txt.splitlines():
... print [float(e) for e in re.search(r'\[([^\]]+)',line).group(1).split(',')]
...
[2.856, 9.678, 6.001]
[8.923, 3.125, 0.588]
[7.122, 9.023, 4.0, 421.0]
You would need to add error code to that (if the match fails for instance) but this is the core of what you are looking for.
BTW: Don't use list as a variable name. You will overwrite the list function and have confusing errors in the future...
line.split() returns a list of strings.
For example:
my_string = 'hello hi'
my_string.split(' ') is equal to ['hello', 'hi']
To put a list of strings, like ['hello', 'hi] back together, use join.
For example, ' '.join(['hello', 'hi']) is equal to 'hello hi'. The ' ' specifies to put a space between all the elements in the list that you are joining.
Assuming a python array "myarray" contains:
mylist = [u'a',u'b',u'c']
I would like a string that contains all of the elements in the array, while preserving the double quotes like this (notice how there are no brackets, but parenthesis instead):
result = "('a','b','c')"
I tried using ",".join(mylist), but it gives me the result of "a,b,c" and eliminated the single quotes.
You were quite close, this is how I would've done it:
result = "('%s')" % "','".join(mylist)
What about this:
>>> mylist = [u'a',u'b',u'c']
>>> str(tuple(map(str, mylist)))
"('a', 'b', 'c')"
Try this:
result = "({})".format(",".join(["'{}'".format(char) for char in mylist]))
>>> l = [u'a', u'b', u'c']
>>> str(tuple([str(e) for e in l]))
"('a', 'b', 'c')"
Calling str on each element e of the list l will turn the Unicode string into a raw string. Next, calling tuple on the result of the list comprehension will replace the square brackets with parentheses. Finally, calling str on the result of that should return the list of elements with the single quotes enclosed in parentheses.
What about repr()?
>>> repr(tuple(mylist))
"(u'a', u'b', u'c')"
More info on repr()
Here is another variation:
mylist = [u'a',u'b',u'c']
result = "\"{0}\"".format(tuple(mylist))
print(result)
Output:
"('a', 'b', 'c')"
How do I concatenate a list of strings into a single string?
For example, given ['this', 'is', 'a', 'sentence'], how do I get "this-is-a-sentence"?
For handling a few strings in separate variables, see How do I append one string to another in Python?.
For the opposite process - creating a list from a string - see How do I split a string into a list of characters? or How do I split a string into a list of words? as appropriate.
Use str.join:
>>> words = ['this', 'is', 'a', 'sentence']
>>> '-'.join(words)
'this-is-a-sentence'
>>> ' '.join(words)
'this is a sentence'
A more generic way (covering also lists of numbers) to convert a list to a string would be:
>>> my_lst = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> my_lst_str = ''.join(map(str, my_lst))
>>> print(my_lst_str)
12345678910
It's very useful for beginners to know
why join is a string method.
It's very strange at the beginning, but very useful after this.
The result of join is always a string, but the object to be joined can be of many types (generators, list, tuples, etc).
.join is faster because it allocates memory only once. Better than classical concatenation (see, extended explanation).
Once you learn it, it's very comfortable and you can do tricks like this to add parentheses.
>>> ",".join("12345").join(("(",")"))
Out:
'(1,2,3,4,5)'
>>> list = ["(",")"]
>>> ",".join("12345").join(list)
Out:
'(1,2,3,4,5)'
Edit from the future: Please don't use the answer below. This function was removed in Python 3 and Python 2 is dead. Even if you are still using Python 2 you should write Python 3 ready code to make the inevitable upgrade easier.
Although #Burhan Khalid's answer is good, I think it's more understandable like this:
from str import join
sentence = ['this','is','a','sentence']
join(sentence, "-")
The second argument to join() is optional and defaults to " ".
list_abc = ['aaa', 'bbb', 'ccc']
string = ''.join(list_abc)
print(string)
>>> aaabbbccc
string = ','.join(list_abc)
print(string)
>>> aaa,bbb,ccc
string = '-'.join(list_abc)
print(string)
>>> aaa-bbb-ccc
string = '\n'.join(list_abc)
print(string)
>>> aaa
>>> bbb
>>> ccc
We can also use Python's reduce function:
from functools import reduce
sentence = ['this','is','a','sentence']
out_str = str(reduce(lambda x,y: x+"-"+y, sentence))
print(out_str)
We can specify how we join the string. Instead of '-', we can use ' ':
sentence = ['this','is','a','sentence']
s=(" ".join(sentence))
print(s)
If you have a mixed content list and want to stringify it, here is one way:
Consider this list:
>>> aa
[None, 10, 'hello']
Convert it to string:
>>> st = ', '.join(map(str, map(lambda x: f'"{x}"' if isinstance(x, str) else x, aa)))
>>> st = '[' + st + ']'
>>> st
'[None, 10, "hello"]'
If required, convert back to the list:
>>> ast.literal_eval(st)
[None, 10, 'hello']
If you want to generate a string of strings separated by commas in final result, you can use something like this:
sentence = ['this','is','a','sentence']
sentences_strings = "'" + "','".join(sentence) + "'"
print (sentences_strings) # you will get "'this','is','a','sentence'"
def eggs(someParameter):
del spam[3]
someParameter.insert(3, ' and cats.')
spam = ['apples', 'bananas', 'tofu', 'cats']
eggs(spam)
spam =(','.join(spam))
print(spam)
Without .join() method you can use this method:
my_list=["this","is","a","sentence"]
concenated_string=""
for string in range(len(my_list)):
if string == len(my_list)-1:
concenated_string+=my_list[string]
else:
concenated_string+=f'{my_list[string]}-'
print([concenated_string])
>>> ['this-is-a-sentence']
So, range based for loop in this example , when the python reach the last word of your list, it should'nt add "-" to your concenated_string. If its not last word of your string always append "-" string to your concenated_string variable.