I am newbie in Python facing a problem: How to insert some fields in already existing string?
For example, suppose I have read one line from any file which contains:
line = "Name Age Group Class Profession"
Now I have to insert 3rd Field(Group) 3 times more in the same line before Class field. It means the output line should be:
output_line = "Name Age Group Group Group Group Class Profession"
I can retrieve 3rd field easily (using split method), but please let me know the easiest way of inserting into the string?
The functions below will allow one to insert one string into another string:
def str_insert(from_me, into_me, at):
"""
Inserts the string <from_me> into <into_me>
Input <at> must be an integer index of <into_me> or a substring of <into_me>
Inserts <from_me> AFTER <at>, not before <at>
Inputs <from_me> and <into_me> must have working __str__ methods defined.
This is satisfied if they already are strings.
If not already strings, <from_me>, <into_me> are converted into strings.
If you try to insert an empty string, that's fine, and the result
is no different from the original.
In order to insert 'from_me' after nothing (insert at the beginning of the string) use:
at = '' or at = 0
"""
try:
return str_insert_or_raise(from_me, into_me, at)
except ValueError as err:
serr = str(err)
if (str_insert_or_raise.__name__ in serr) and 'not found' in serr and '<at>' in serr:
# if can't find where to insert stuff, don't bother to insert it
# use str_insert_or_raise if you want an exception instead
return into_me
else:
raise err
##############################################################
def str_insert_or_raise(from_me, into_me, at):
"""
Inserts the string <from_me> into <into_me>
Inserts <from_me> AFTER <at>, not before <at>
Input <at> must be an integer index of <into_me> or a substring of <into_me>
If <at> is the string '15', that substring will be searched for,
'15' will not be interpreted as an index/subscript.
Inputs <from_me> and <into_me> must have working __str__ methods defined.
If not already strings, <from_me>, <into_me> are converted into strings.
If you try to insert something, but we cannot find the position where
you said to insert it, then an exception is thrown guaranteed to at least
contain the following three substrings:
str_insert_or_raise.__name__
'not found'
'<at>'
"""
try:
if isinstance(at, int):
return str_insert_by_int(from_me, into_me, at)
# Below, the calls to str() work fine if <at> and <from_me> are already strings
# it makes them strings if they are not already
return str_insert_by_str(str(from_me), str(into_me), str(at))
except ValueError as err:
serr = str(err)
if 'empty string' in serr:
return into_me # We allow insertion of the empty string
elif ("<at>" in serr) and 'not found' in serr:
msg_start = "In " + str_insert_or_raise.__name__ + ": "
msg = [msg_start, "\ninput ", "<at> string", " not found in ", "<into_me>",
"\ninput <", str(at) , "> not found in <", str(into_me), ">"]
msg = ''.join(msg)
raise ValueError(msg) from None
else:
raise err
#############################################################
def str_insert_by_str(from_me, into_me, at):
"""
Inserts the string <from_me> into <into_me>
puts 'from_me' AFTER 'at', not before 'at'
For example,
str_insert_or_raise(at = '2', from_me = '0', into_me = '123')
puts the zero after the 2, not before the 2
The call returns '1203' not '1023'
Throws exceptions if input arguments are not strings.
Also, if <from_me> is empty or <at> is not a substring of <into_me> then
an exception is raised.
For fewer exceptions, use <str_insert_or_raise> instead.
"""
try:
s = into_me.replace(at, at + from_me, 1)
except TypeError as terr: # inputs to replace are not strings
msg_list = ['Inputs to function ', str_insert_by_str.__name__, '() must be strings']
raise TypeError(''.join(msg_list)) from None
# At the end of call to replace(), the '1' indicates we will replace
# the leftmost occurrence of <at>, instead of every occurrence of <at>
if (s == into_me): # <at> string not found and/or <from_me> is the empty string
msg_start = "In " + str_insert_by_str.__name__ + ": "
if from_me == '':
msg = ''.join([msg_start, "attempted to insert an empty string"])
raise ValueError(msg) from None
raise ValueError(msg_start, "Input <at> string not found in <into_me>.",
"\nUnable to determine where you want the substring inserted.") from None
return s
##################################################
def str_insert_by_int(from_me, into_me, at):
"""
* Inserts the string <from_me> into <into_me> at integer index <at>
* throws exceptions if input arguments are not strings.
* Also, throws an exception if you try to insert the empty string
* If <at> is less than zero, <from_me> gets placed at the
beginning of <into_me>
* If <at> is greater than the largest index of <into_me>,
<from_me> gets placed after the end of <into_me>
For fewer exceptions, use <str_insert_or_raise> instead.
"""
at = into_me[:(at if at > 0 else 0)]
return str_insert_by_str(from_me, into_me, at)
The code below demonstrates how to call the str_insert function given earlier
def foo(*args):
return args
F = 'F. '
s = 'Using the string \'John \' to specify where to make the insertion'
result = str_insert(from_me = F, into_me ='John Kennedy', at ='John ')
print(foo('\n\n', s, '\n', result))
s = 'Using an int returned by find(\'Ken\') to specify where to make the insertion'
index = 'John Kennedy'.find('Ken') # returns the position of the first letter of 'Ken', not the last letter
result = str_insert(from_me = F, into_me ='John Kennedy', at = index)
print(foo('\n\n', s, '\n', result))
s = 'Using an int (5) to specify where to make the insertion.'
result = str_insert(from_me = F, into_me ='John Kennedy', at = 5)
print(foo('\n\n', s, '\n', result))
s = "Looking for an 'at' string which does not exist"
result = str_insert(from_me = F, into_me ='John Kennedy', at ='x')
print(foo('\n\n', s, '\n', result))
s = ''.join(["Looking for the empty string.",
"\nFind one immediately at the beginning of the string"])
result = str_insert(from_me = F, into_me ='John Kennedy', at = '')
print(foo('\n\n', s, '\n', result))
s = "Insert an empty string at index 3. No visible change"
result = str_insert(from_me = '', into_me = 'John Kennedy', at = 3)
print(foo('\n\n', s, '\n', result))
for index in [-5, -1, 0, 1, 997, 999]:
s = "index " + str(index)
result = str_insert(from_me = F, into_me = 'John Kennedy', at = index)
print(foo('\n\n', s, '\n', result))
None of the functions above will modify a string "in-place." The functions each return a modified copy of the string, but the original string remains intact.
For example,
s = ''.join(["Below is what we get when we forget ",
"to overwrite the string with the value",
" returned by str_insert_or_raise:"])
examp_str = 'John Kennedy'
str_insert('John ', F, examp_str)
print(foo('\n\n', s, '\n', examp_str))
# examp_str is still 'John Kennedy' without the F
I had a similar problem for my DNA assignment and I used bgporter's advice to answer it. Here is my function which creates a new string...
def insert_sequence(str1, str2, int):
""" (str1, str2, int) -> str
Return the DNA sequence obtained by inserting the
second DNA sequence into the first DNA sequence
at the given index.
>>> insert_sequence('CCGG', 'AT', 2)
CCATGG
>>> insert_sequence('CCGG', 'AT', 3)
CCGATG
>>> insert_sequence('CCGG', 'AT', 4)
CCGGAT
>>> insert_sequence('CCGG', 'AT', 0)
ATCCGG
>>> insert_sequence('CCGGAATTGG', 'AT', 6)
CCGGAAATTTGG
"""
str1_split1 = str1[:int]
str1_split2 = str1[int:]
new_string = str1_split1 + str2 + str1_split2
return new_string
There are several ways to do this:
One way is to use slicing:
>>> a="line=Name Age Group Class Profession"
>>> b=a.split()
>>> b[2:2]=[b[2]]*3
>>> b
['line=Name', 'Age', 'Group', 'Group', 'Group', 'Group', 'Class', 'Profession']
>>> a=" ".join(b)
>>> a
'line=Name Age Group Group Group Group Class Profession'
Another would be to use regular expressions:
>>> import re
>>> a=re.sub(r"(\S+\s+\S+\s+)(\S+\s+)(.*)", r"\1\2\2\2\2\3", a)
>>> a
'line=Name Age Group Group Group Group Class Profession'
I know it's malapropos, but IMHO easy way is:
def insert (source_str, insert_str, pos):
return source_str[:pos]+insert_str+source_str[pos:]
An important point that often bites new Python programmers but the other posters haven't made explicit is that strings in Python are immutable -- you can't ever modify them in place.
You need to retrain yourself when working with strings in Python so that instead of thinking, "How can I modify this string?" instead you're thinking "how can I create a new string that has some pieces from this one I've already gotten?"
line='Name Age Group Class Profession'
arr = line.split()
for i in range(3):
arr.insert(2, arr[2])
print(' '.join(arr))
Answer for Insert characters of string in other string al located positions
str1 = "ibuprofen"
str2 = "MEDICAL"
final_string=""
Value = 2
list2=[]
result=[str1[i:i+Value] for i in range(0, len(str1), Value)]
count = 0
for letter in result:
if count < len(result)-1:
final_string = letter + str2[count]
list2.append(final_string)
elif ((len(result)-1)==count):
list2.append(letter + str2[count:len(str2)])
break
count += 1
print(''.join(list2))
For the sake of future 'newbies' tackling this problem, I think a quick answer would be fitting to this thread.
Like bgporter said: Python strings are immutable, and so, in order to modify a string you have to make use of the pieces you already have.
In the following example I insert 'Fu' in to 'Kong Panda', to create 'Kong Fu Panda'
>>> line = 'Kong Panda'
>>> index = line.find('Panda')
>>> output_line = line[:index] + 'Fu ' + line[index:]
>>> output_line
'Kong Fu Panda'
In the example above, I used the index value to 'slice' the string in to 2 substrings: 1 containing the substring before the insertion index, and the other containing the rest. Then I simply add the desired string between the two and voilà, we have inserted a string inside another.
Python's slice notation has a great answer explaining the subject of string slicing.
Source: Stackoverflow.com