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.
Related
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.
I am trying to read .ini file with keywords having single items or list items. When I try to print single item strings and float values, it prints as h,e,l,l,o and 2, ., 1 respectively, whereas it should have been just hello and 2.1. Also, when I try to write new single item string/float/integer, there is , at the end. I am new to python and dealing with configobj. Any help is appreciated and if this question has been answered previously, please direct me to it. Thanks!
from configobj import ConfigObj
Read
config = ConfigObj('para_file.ini')
para = config['Parameters']
print(", ".join(para['name']))
print(", ".join(para['type']))
print(", ".join(para['value']))
Write
new_names = 'hello1'
para['name'] = [x.strip(' ') for x in new_names.split(",")]
new_types = '3.1'
para['type'] = [x.strip(' ') for x in new_types.split(",")]
new_values = '4'
para['value'] = [x.strip(' ') for x in new_values.split(",")]
config.write()
My para_file.ini looks like this,
[Parameters]
name = hello1
type = 2.1
value = 2
There are two parts to your question.
Options in ConfigObj can be either a string, or a list of strings.
[Parameters]
name = hello1 # This will be a string
pets = Fluffy, Spot # This will be a list with 2 items
town = Bismark, ND # This will also be a list of 2 items!!
alt_town = "Bismark, ND" # This will be a string
opt1 = foo, # This will be a list of 1 item (note the trailing comma)
So, if you want something to appear as a list in ConfigObj, you must make sure it includes a comma. A list of one item must have a trailing comma.
In Python, strings are iterable. So, even though they are not a list, they can be iterated over. That means in an expression like
print(", ".join(para['name']))
The string para['name'] will be iterated over, producing the list ['h', 'e', 'l', 'l', 'o', '1'], which Python dutifully joins together with spaces, producing
h e l l o 1
These commands:
l = ["1\n2"]
print(l)
print
['1\n2']
I want to print
['1
2']
Is it possible when we generate the list outside of the print() command?
A first attempt:
l = ["1\n2"]
print(repr(l).replace('\\n', '\n'))
The solution above doesn't work in tricky cases, for example if the string is "1\\n2" it replaces, but it shouldn't. Here is how to fix it:
import re
l = ["1\n2"]
print(re.sub(r'\\n|(\\.)', lambda match: match.group(1) or '\n', repr(l)))
Only if you are printing the element itself (or each element) and not the whole list:
>>> a = ['1\n2']
>>> a
['1\n2']
>>> print a
['1\n2']
>>> print a[0]
1
2
When you try to just print the whole list, it prints the string representation of the list. Newlines belong to individual elements so get printed as newlines only when print that element. Otherwise, you will see them as \n.
You should probably use this, if you have more than one element
>>> test = ['1\n2', '3', '4\n5']
>>> print '[{0}]'.format(','.join(test))
[1
2,3,4
5]
Try this:
s = ["1\n2"]
print("['{}']".format(s[0]))
=> ['1
2']
File abc's content:
a
b
c
The code is
data_fh = open("abc")
str = data_fh.read()
arr = str.split("\n")
print len(arr)
data_fh.seek(0)
arr = data_fh.read().splitlines()
print len(arr)
but the output is:
4
3
so why is that?
Because .splitlines() does not include the empty line at the end, while .split('\n') returns an empty string for the last ...\n:
>>> 'last\n'.split('\n')
['last', '']
>>> 'last\n'.splitlines()
['last']
This is explicitly mentioned in the str.splitlines() documentation:
Unlike split() when a delimiter string sep is given, this method returns an empty list for the empty string, and a terminal line break does not result in an extra line.
If there is no trailing newline, the output is identical:
>>> 'last'.split('\n')
['last']
>>> 'last'.splitlines()
['last']
In other words, str.split() doesn't add anything, but str.splitlines() does remove.
You probably have a trailing newline:
>>> s = 'a\nb\nc\n' # <-- notice the \n at the end
>>>
>>> s.split('\n')
['a', 'b', 'c', '']
>>>
>>> s.splitlines()
['a', 'b', 'c']
Notice that split() leaves an empty string at the end whereas splitlines() does not.
As an aside, you shouldn't use str as a variable name since that's already taken by a built-in function.
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.