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Passed argument memory context

I came across this while coding:
def interpret(command):
# comment1: command.replace("()","o").replace("(al)","al")
# comment2: print(command)
res = command.replace("()","o").replace("(al)","al")
print(res)
interpret("G()(al)")
In the above code, I was expecting the string to be replaced at 'comment1' but, I got the same value passed as an argument i.e. "G()(al)" but on storing it in a different location (here, 'res') I was able to get the expected result.
Could you please point out what made Python remember the 'command' original value or is there something like JavaScript's closure or I am unable to see the simple point here?

According to the official documentation:
str.replace(old, new[, count])
Return a copy of the string with all occurrences of substring old replaced by new. If the optional argument count is given, only the first count occurrences are replaced.
Meaning that a new string is created for the data to be stored in. And since you did not store the result of the replacement operations back into the command parameter, the result is never used. Storing the data in another variable res also works and might provide more bug-resistance if you want to perform multiple operations on command that you might re-arrange later on.

In flask, Is it possible to use url convertor without splitting them using slash '/'?

I have a route:
#app.route("/login/<user>/<timestamp>")
def user(user, timestamp):.
But, I need it in this form -
#app.route("/login/<user><timestamp>")
def user(user, timestamp):.
i.e without the slash('/').
Is there any way to do it ?

Short answer: It is possible given the two parameters have a non-overlapping pattern. By giving it a wildcard-pattern however (you did not specify the converter). It will result in the fact that all content is handled to the user. That being said, it is advisable to have a clear separator.
As is specified in the documentation, you can define variables by writing them like HTML tags, like <var>, you can also specify a converter, like <converter:var>. If you do not specify a converter, the parameter is assumed to be a string that can not contain slashes.
There are however other converters, like int, float, path and uuid.
If the patterns are written in such way that it is clear when the first pattern ends, and the second pattern begins, then it this can be handled. For example:
#app.route("/login/<int:day><user>")
can work, given user can not start with a digit, since here once the sequence of digits ends, Flask will parse the <user> parameter.
By writing #app.route("/login/<user><timestamp>") however, the two patterns are overlapping: if we do not have a parsing strategy any split could be a valid one. Since the engine is greedy if I recall correctly, in practice it will result in the fact that user takes all characters, and timestamp none.
Since the default string does not include a slash, we know that the slash acts as a clear separator, since it is not included in both variables in your example.

Is it possible to declare a variable with a value for string and a placeholder in python?

I am trying to initialize a long string value to a variable, but this string has a word that can not be constant, like this example.
Say I want to store a string like this.
str = "https://stackoverflow.com/users/7833397/meskerem"
But assume the number 7833397 will change over time, so I am trying to find a way to store the string while making making a wildcard for the number. But I am not sure if this can be done in Python

Use the format method.
template = "https://stackoverflow.com/users/{0}/meskerem"
# Lots of stuff happens here
url = template.format("7833397")
The format method supports its own little mini language, and depending on your use-case you may find it more intuitive to name the various parts of your template, too:
template = "https://stackoverflow.com/users/{id}/{username}"
# Lots of stuff happens here
url = template.format(id="7833397", username="meskerem")

First, avoid usign the identifier str. Second, you can put placeholders in strings using two methods of string formatting:
Old style
The "old" style uses C-style string formatting syntax, and "modulo" operation on the string to do the actual insertion. You can pass multiple replacements as a tuple:
s = "foo%sbaz" # expects a string
print(s%"bar")
s2 = "foo%s%d"
print(s2%("bar", 2))
New style
The "new" style uses a generic {} which can be filled using the str.format() method. Multiple replacements are passed as a unzipped tuple, i.e. as mutiple arguments:
s = "foo{}baz" # can be "anything"
print(s.format("bar"))
s2 = "foo{}{}"
print(s2.format("bar", 2))
This site might come handy as a reference.

You can use '%s'(string formatting syntax )
modified_str = "https://stackoverflow.com/users/%s/meskerem" % (number,)

Advanced functions in Django templates?

I need to add a <br/> after each character in a string which I'm passing into the template. While one way of doing it would involve doing it before it is passed into the template (i.e. in the Python code), I'm wondering if it is possible to do it in the actual template.
Or would I be better off creating a helper function and invoking it from the template, and if so, how would I import that function/module into the template.
The one thing I want to avoid is mixing HTML bits with the view code so adding the <br/>s in the view should only be the last resort.

Strings in Python are sequences, therefore the individual characters in them can be joined.

How about you make such a function in the javascript, and after passing the string to the template, instead of using it directly, you can call that function on the string, and the function returns the string with every character is followed by a <br/>?
var nStr = "";
for (i=0;i<str.length;i++)
{
nStr = nStr.concat(str.charAt(i),"<br/>");
}

Getting two strings in variable from URL in Django

I'm having some trouble sending along more than one variable to the view.
my urls.py is as follows:
urlpatterns = patterns('',
url(r'^rss/(?P<anything>[^/]+)/$', 'rss.rssama.views.makerss', name='anything'),
url(r'^$', 'rss.rssama.views.home'),
)
views.py
def maakrss(request, anything):
So now it takes from www.mydomain.com/rss/[anything]/ and sends 'anything' to my view. However I also want it to send along another string to views.py, like:
www.mydomain.com/rss/[anynumber]/[anystring]/
I tried this but that didn't work:
url(r'^rss/(?P<anynumber>[^/]+)/(?P<anystring>[^/]+)/$', 'rss.rssama.views.makerss', name='anynumber', name2='anystring'),
But this doesn't work, it gives this error: keyword argument repeated (urls.py, line 17)
So my question: How can I make it to give along two string from the url?

To begin with, the regex part should look like this:
r'^/rss/(?P<anynumber>\d+)/(?P<anystring>.+)/$'
Those strings inside the <...> parts allow you to give a name to whatever the regex matches. Django will then use that name to pass the value to your function. Therefore your function must have an argument with the same name. In this case, Django will take the value called anynumber and use that value for the parameter of your function that is called anynumber. The same goes for anystring, and this system frees you from worrying about what order the arguments of your function are in.
\d+ will match one or more numeric characters (digits). It's good practice to limit the regex to match only numbers if that's what you intend to catch, rather than any character and hope that only numbers appear. If you wanted to limit the digits part to a certain number of digits, you could use \d{1,4} to take from one to four digits.
The next part, (?P<anystring>.+) will catch a string consisting of one or more of any characters. This would actually match something like 'letters/moreletters', including the slash. There are a number of "special sequences" in Python regex that might help. To match only digits, letters, and the underscore character, use \w, as in (?P<anystring>\w+). To be more lax but ignore whitespace or any other non-sense, (?P<anystring>[a-zA-Z1-9:;_{}\[\]] to catch a whole slew of characters. Make sure to escape anything that might be a special character in a regex. However, be conservative. If you allow too many options who knows what sorts of bugs you'll have to work out later.
Now onto name parameter of the url function. That name is not what it will pass the caught patterns to your functions as. It's a name for a particular class of invocation of your view function that can be used as a short-hand in other contexts like, the template tag {% url view-name arg1 arg2 %}. So, the name you have already, "anything", refers to a call to your view function, passing it one keyword argument that happens to be called anything. For the case where you want to pass two strings, give that a name like "rss-number-string" to signify the arguments you want to take, or a name that refers to the special function your view will be performing with that combination.
I use multiple names for the same function all the time, and the key is this:
def makerss(request, anystring=None, anynumber=None):
By giving the parameters default values, it allows you to use the same function in different ways. In this case, the function can be used when you only want to pass a value for anystring, or when anystring and anynumber should have values.
I know this is a lot of different points, so I'll try to put it all together so you can see how it might work. To have two urls, one which catch a string and passes it on, and another which catches a number, a slash, and then a string, but both point to the same view function, you could use this:
urlpatterns = patterns('',
url(r'^rss/(?P<anystring>\w+)/$', 'rss.rssama.views.makerss', name='rss-anystring'),
url(r'^rss/(?P<anynumber>\d+)/(?P<anystring>\w+)/$', 'rss.rssama.views.makerss', name='rss-number-string'),
url(r'^$', 'rss.rssama.views.home'),
)
With a view function something like this:
def makerss(request, anystring=None, anynumber=None):
if anystring:
if anynumber:
#Do something with the string and the number
else:
#Do something with just the string
Please let me know if this helps. Also, Django rocks, so kudos!
Python Regex Library Docs

You don't really need to give two name arguments for this. I mean, you already have the variable names inside regex. The actual problem is, you cannot give two name arguments, so you can do this instead:
url(r'^rss/(?P<anynumber>[^/]+)/(?P<anystring>[^/]+)/$', 'rss.rssama.views.makerss',name='something'),
EDIT:
using the urlConf above you can create corresponding view as:
def makerss(request, anynumber, anystring):

What is name2 supposed to be? The url function takes a name parameter, which is the name of the URL when you reverse it, but you can't put random extra functions.
Otherwise, you have the right syntax for sending two elements to a view. Of course, since you've masked the variable names and not provided the actual error or traceback, we have no way of knowing what really is going wrong.