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How to put condition for string not to follow each other [duplicate]

I tried this code to do simple string replacement:
X = "hello world"
X.replace("hello", "goodbye")
Why doesn't X change, from "hello world" to "goodbye world"?

This is because strings are immutable in Python.
Which means that X.replace("hello","goodbye") returns a copy of X with replacements made. Because of that you need replace this line:
X.replace("hello", "goodbye")
with this line:
X = X.replace("hello", "goodbye")
More broadly, this is true for all Python string methods that change a string's content "in-place", e.g. replace,strip,translate,lower/upper,join,...
You must assign their output to something if you want to use it and not throw it away, e.g.
X = X.strip(' \t')
X2 = X.translate(...)
Y = X.lower()
Z = X.upper()
A = X.join(':')
B = X.capitalize()
C = X.casefold()
and so on.

All string functions as lower, upper, strip are returning a string without modifying the original. If you try to modify a string, as you might think well it is an iterable, it will fail.
x = 'hello'
x[0] = 'i' #'str' object does not support item assignment
There is a good reading about the importance of strings being immutable: Why are Python strings immutable? Best practices for using them

Example for String Methods
Given a list of filenames, we want to rename all the files with extension hpp to the extension h. To do this, we would like to generate a new list called newfilenames, consisting of the new filenames.
filenames = ["program.c", "stdio.hpp", "sample.hpp", "a.out", "math.hpp", "hpp.out"]
# Generate newfilenames as a list containing the new filenames
# using as many lines of code as your chosen method requires.
newfilenames = []
for i in filenames:
if i.endswith(".hpp"):
x = i.replace("hpp", "h")
newfilenames.append(x)
else:
newfilenames.append(i)
print(newfilenames)
# Should be ["program.c", "stdio.h", "sample.h", "a.out", "math.h", "hpp.out"]

Break the string (udacity: Intro to python ) [duplicate]

I wrote a quick script to remove the 'http://' substring from a list of website addresses saved on an excel column. The function replace though, doesn't work and I don't understand why.
from openpyxl import load_workbook
def rem(string):
print string.startswith("http://") #it yields "True"
string.replace("http://","")
print string, type(string) #checking if it works (it doesn't though, the output is the same as the input)
wb = load_workbook("prova.xlsx")
ws = wb["Sheet"]
for n in xrange(2,698):
c = "B"+str(n)
print ws[c].value, type(ws[c].value) #just to check value and type (unicode)
rem(str(ws[c].value)) #transformed to string in order to make replace() work
wb.save("prova.xlsx") #nothing has changed

String.replace(substr)
does not happen in place, change it to:
string = string.replace("http://","")

string.replace(old, new[, max]) only returns a value—it does not modify string. For example,
>>> a = "123"
>>> a.replace("1", "4")
'423'
>>> a
'123'
You must re-assign the string to its modified value, like so:
>>> a = a.replace("1", "4")
>>> a
'423'
So in your case, you would want to instead write
string = string.replace("http://", "")

function call the convert a list is alpha characters to numeric

I am trying a manual implementation of the Soundex Algorithm and this requires converting alpha text characters to numeric text characters. I have defined the following function:
import re
def sub_pattern(text):
sub = [str(i) for i in range(1,4)]
string = text
abc = re.compile('[abc]')
xyz = re.compile('[xyz]')
encode = [abc, xyz]
encode_iter = iter(encode)
alpha_search = re.compile('[a-zA-Z]')
for i in sub:
if alpha_search.search(string):
pattern = next(encode_iter)
string = pattern.sub(i, string)
else:
return(string)
This function will encode abc characters to 1 and xyz characters to 2. However, it only works for a single string and I need to pass a list of strings to the function. I've gotten the results I want using:
list(map(sub_pattern, ['aab', 'axy', 'bzz']
But I want to be able to pass the list to the function directly. I've tried this with no success as it ends only returning the first string from the list.
def sub_pattern(text_list):
all_encoded = []
sub = [str(i) for i in range(1,4)]
abc = re.compile('[abc]')
xyz = re.compile('[xyz]')
encode = [abc, xyz]
encode_iter = iter(encode)
alpha_search = re.compile('[a-zA-Z]')
for string in text_list:
for i in sub:
if alpha_search.search(string):
pattern = next(encode_iter)
string = pattern.sub(i, string)
else:
all_encoded.append(string)
A couple things to note:
Because I am implementing the Soundex Algorithm, the order of the text when I encode it matters. I would prefer to update the string character at its orginal index to avoid having to reorganize it afterwards. In other words, you can't do any sorting to the string...I've created the iterator to incrementally update the string and it only grabs the next regex pattern if all the characters have not already been converted.
This function will be a part of two custom classes that I am creating. Both will call the __iter__ method so that I can created the iterable. That's why I use the iter() function to create an iterable because it will create a new instance if the iterator automatically.
I know this may seem like a trivial issue relative to what I'm doing, but I'm stuck.
Thank you in advance.

How about using your own function recursively? You get to keep the original exactly as it is, in case you needed it:
import re
def sub_pattern(text):
if isinstance(text, str):
sub = [str(i) for i in range(1,4)]
string = text
abc = re.compile('[abc]')
xyz = re.compile('[xyz]')
encode = [abc, xyz]
encode_iter = iter(encode)
alpha_search = re.compile('[a-zA-Z]')
for i in sub:
if alpha_search.search(string):
pattern = next(encode_iter)
string = pattern.sub(i, string)
else:
return(string)
else:
return([sub_pattern(t) for t in text])
print(list(map(sub_pattern, ['aab', 'axy', 'bzz']))) # old version still works
print(sub_pattern(['aab', 'axy', 'bzz'])) # new version yields the same result
Should a reader don't know what recursively means: calling a function from within itself.
It is allowed because each function call creates its own
scope,
it can be useful when you can solve a problem by performing a simple operation multiple times, or can't predict in advance how many times you need to perform it to reach your solution, e.g. when you need to unpack nested structures
it is defined by choosing a base case (the solution), and call the function in all other cases until you reach your base case.

I assume the issue with your example was, that once you traversed the iterator, you ran into StopIteration for the next string.
I'm not sure this is what you want, but I would create a new iterator for each string, since you have to be able to traverse over all of it for every new item. I tweaked some variable names that may cause confusion, too (string and sub). See comments for changes:
def sub_pattern(text_list):
all_encoded = []
digits = [str(i) for i in range(1,4)]
abc = re.compile('[abc]')
xyz = re.compile('[xyz]')
encode = [abc, xyz]
alpha_search = re.compile('[a-zA-Z]')
for item in text_list:
# Create new iterator for each string.
encode_iter = iter(encode)
for i in digits:
if alpha_search.search(item):
pattern = next(encode_iter)
item = pattern.sub(i, item)
else:
all_encoded.append(item)
# You likely want appending to end once no more letters can be found.
break
# Return encoded texts.
return all_encoded
Test:
print(sub_pattern(['aab', 'axy', 'bzz'])) # Output: ['111', '122', '122']

Replace() not working [duplicate]

I tried this code to do simple string replacement:
X = "hello world"
X.replace("hello", "goodbye")
Why doesn't X change, from "hello world" to "goodbye world"?

This is because strings are immutable in Python.
Which means that X.replace("hello","goodbye") returns a copy of X with replacements made. Because of that you need replace this line:
X.replace("hello", "goodbye")
with this line:
X = X.replace("hello", "goodbye")
More broadly, this is true for all Python string methods that change a string's content "in-place", e.g. replace,strip,translate,lower/upper,join,...
You must assign their output to something if you want to use it and not throw it away, e.g.
X = X.strip(' \t')
X2 = X.translate(...)
Y = X.lower()
Z = X.upper()
A = X.join(':')
B = X.capitalize()
C = X.casefold()
and so on.

All string functions as lower, upper, strip are returning a string without modifying the original. If you try to modify a string, as you might think well it is an iterable, it will fail.
x = 'hello'
x[0] = 'i' #'str' object does not support item assignment
There is a good reading about the importance of strings being immutable: Why are Python strings immutable? Best practices for using them

Example for String Methods
Given a list of filenames, we want to rename all the files with extension hpp to the extension h. To do this, we would like to generate a new list called newfilenames, consisting of the new filenames.
filenames = ["program.c", "stdio.hpp", "sample.hpp", "a.out", "math.hpp", "hpp.out"]
# Generate newfilenames as a list containing the new filenames
# using as many lines of code as your chosen method requires.
newfilenames = []
for i in filenames:
if i.endswith(".hpp"):
x = i.replace("hpp", "h")
newfilenames.append(x)
else:
newfilenames.append(i)
print(newfilenames)
# Should be ["program.c", "stdio.h", "sample.h", "a.out", "math.h", "hpp.out"]

Why doesn't calling a string method (such as .replace or .strip) modify (mutate) the string?

I tried this code to do simple string replacement:
X = "hello world"
X.replace("hello", "goodbye")
Why doesn't X change, from "hello world" to "goodbye world"?

This is because strings are immutable in Python.
Which means that X.replace("hello","goodbye") returns a copy of X with replacements made. Because of that you need replace this line:
X.replace("hello", "goodbye")
with this line:
X = X.replace("hello", "goodbye")
More broadly, this is true for all Python string methods that change a string's content "in-place", e.g. replace,strip,translate,lower/upper,join,...
You must assign their output to something if you want to use it and not throw it away, e.g.
X = X.strip(' \t')
X2 = X.translate(...)
Y = X.lower()
Z = X.upper()
A = X.join(':')
B = X.capitalize()
C = X.casefold()
and so on.

All string functions as lower, upper, strip are returning a string without modifying the original. If you try to modify a string, as you might think well it is an iterable, it will fail.
x = 'hello'
x[0] = 'i' #'str' object does not support item assignment
There is a good reading about the importance of strings being immutable: Why are Python strings immutable? Best practices for using them

Example for String Methods
Given a list of filenames, we want to rename all the files with extension hpp to the extension h. To do this, we would like to generate a new list called newfilenames, consisting of the new filenames.
filenames = ["program.c", "stdio.hpp", "sample.hpp", "a.out", "math.hpp", "hpp.out"]
# Generate newfilenames as a list containing the new filenames
# using as many lines of code as your chosen method requires.
newfilenames = []
for i in filenames:
if i.endswith(".hpp"):
x = i.replace("hpp", "h")
newfilenames.append(x)
else:
newfilenames.append(i)
print(newfilenames)
# Should be ["program.c", "stdio.h", "sample.h", "a.out", "math.h", "hpp.out"]