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Short for loop for fetching bash users

A short python script i wrote to fetch users who are using bash. below is script. I don't know why its not working. Please share your ideas as to how this program is working inside.I am beginner in python and looking for lectures on data structures and algorithms. any answers are welcome. Thanks
f = open("/etc/passwd")
mainshell = '/bin/bash'
for line in f:
field = line.split(:)
shell = field[-1]
user = field[0]
if shell = mainshell:
print(user)
edit: I am getting no output. I tried to fetch values of variable shell and users and that exactly what i need but somehow if block is not working. Its not giving any error but just not working.

You are almost there with your script. But there are 2 reasons why its not working.
Your if statement is not doing a string comparison. You should be using == not =
You compare the string mainshell with shell, but you assume shell does not contain whitespaces. But the string will probably look like this /bin/bash (notice the whitespaces at the end?). This can be removed with shell = field[-1].strip()
I think then your program should work fine :)

How to solve "ECitMatch() got multiple values for argument 'bdata'"?

I am new to use bioservices Python package. Now I am going to use that to retrieve PMIDs for two citations, given the specified information and this is the code I have tried:
from bioservices import EUtils
s = EUtils()
print(s.ECitMatch("pubmed",retmode="xml", bdata="proc+natl+acad+sci+u+s+a|1991|88|3248|mann+bj|Art1|%0Dscience|1987|235|182|palmenberg+ac|Art2|"))
But it occurs an error:
"TypeError: ECitMatch() got multiple values for argument 'bdata'".
Could anyone help me to solve that problem?

I think the issue is that you have an unnamed argument (pubmed); if you look at the source code, you can see that the first argument should be bdata; if you provide the arguments like you do, it is, however, unclear whether bdata is "pubmed" or the named argument bdata, therefore the error you obtain.
You can reproduce it with this minimal example:
def dummy(a, b):
return a, b
dummy(10, a=3)
will return
TypeError: dummy() got multiple values for argument 'a'
If you remove "pubmed", the error disappears, however, the output is still incomplete:
from bioservices import EUtils
s = EUtils()
print(s.ECitMatch("proc+natl+acad+sci+u+s+a|1991|88|3248|mann+bj|Art1|%0Dscience|1987|235|182|palmenberg+ac|Art2|"))
returns
'proc+natl+acad+sci+u+s+a|1991|88|3248|mann+bj|Art1|2014248\n'
so only the first publication is taken into account. You can get the results for both by using the correct carriage return character \r:
print(s.ECitMatch(bdata="proc+natl+acad+sci+u+s+a|1991|88|3248|mann+bj|Art1|\rscience|1987|235|182|palmenberg+ac|Art2|"))
will return
proc+natl+acad+sci+u+s+a|1991|88|3248|mann+bj|Art1|2014248
science|1987|235|182|palmenberg+ac|Art2|3026048
I think you neither have to specify retmod nor the database (pubmed); if you look at the source code I linked above you can see:
query = "ecitmatch.cgi?db=pubmed&retmode=xml"
so seems it always uses pubmed and xml.

Two issues here: syntaxic and a bug.
The correct syntax is:
from bioservices import EUtils
s = EUtils()
query = "proc+natl+acad+sci+u+s+a|1991|88|3248|mann+bj|Art1|%0Dscience|1987|235|182|palmenberg+ac|Art2|"
print(s.ECitMatch(query))
Indeed, the underlying service related to ICitMatch has only one database (pubmed) and one format (xml) hence, those 2 parameters are not available : there are hard-coded. Therefore, only one argument is required: your query.
As for the second issue, as pointed above and reported on the bioservices issues page, your query would return only one publication. This was an issue with the special character %0D (in place of a return carriage) not being interpreted corectly by the URL request. This carriage character (either \n, \r or %0d) is now taken into account in the latest version on github or from pypi website if you use version 1.7.5
Thanks to willigot for filling the issue on bioservices page and bringing it to my attention.
disclaimer: i'm the main author of bioservices

Python 3.3 library abpy, file undefined

I'm using a library ABPY (library here) for python but it is in older version i think. I'm using Python 3.3.
I did fix some PRINT errors, but that's how much i know, I'm really new on programing.
I want to fetch some webpage and filter it from advertising and then print it again.
EDITED after Sg'te'gmuj told me how to convert from python 2.x to 3.x this is my new code:
#!/usr/local/bin/python3.1
import cgitb;cgitb.enable()
import urllib.request
response = urllib.request.build_opener()
response.addheaders = [('User-agent', 'Mozilla/5.0')]
response = urllib.request.urlopen("http://www.youtube.com")
html = response.read()
from abpy import Filter
with open("easylist.txt") as f:
ABPFilter = Filter(file('easylist.txt'))
ABPFilter.match(html)
print("Content-type: text/html")
print()
print (html)
Now it is displaying a blank page

Just took a peek at the library, it seems that the file "easylist.txt" does not exist; you need to create the file, and populate it with the appropriate filters (in whatever format ABP specifies).
Additionally, it appears it takes a file object; try something like this instead:
with open("easylist.txt") as f:
ABPFilter = Filter(f)
I can't say this is wholly accurate though since I have no experience with the library, but looking at it's code I'd suspect either of the two are the problem, if not both.
Addendum #1
Looking at the code more in-depth, I have to agree that even if that fix I supplied does work, you're going to have more problems (it's in 2.x as you suggested, when you're using 3.x). I'd suggest utilizing Python's 2to3 function, to convert from typical Python 2 to Python 3 code (it's not foolproof though). The command line would be as so:
2to3 -w abpy.py
That will convert it from Python 2.x to 3.x code, and re-write the source file.
Addendum #2
The code to pass the file object should be the "f" variable, as shown above (modified to represent that; I wasn't paying attention and just left the old file function call in the argument).
You need to pass a URI to the function as well:
ABPFilter.match(URI)
You'll need to modify the code to pass those items into an array (I'm assuming at least); I'm playing with it now to see. At present I'm getting a rule error (not a Python error; but merely error handling used by abpy.py, which is good because it suggests that it's the right train of thought).
The code for the Filter.match function is as following (after using the 2to3 Python script):
def match(self, url, elementtype=None):
tokens = RE_TOK.split(url)
print(tokens)
for tok in tokens:
if len(tok) > 2:
if tok in self.index:
for rule in self.index[tok]:
if rule.match(url, elementtype=elementtype):
print(str(rule))
What this means is you're, at present, at a point where you need to program the functionality; it appears this module only indicates the rule. However, that is still useful.
What this means is that you're going to have to modify this function to take the HTML, in place of the the "url" parameter. You're going to regex the HTML (this may be rather intensive) for a list of URIs and then run each item through the match loop Where you go from there to actually filter the nodes, I'm not sure; but there is a list of filter types, so I'm assuming there is a typical procedural ABP does to remove the nodes (possibly, in some cases merely by removing the given URI from the HTML?)
References
http://docs.python.org/3.3/library/2to3.html

Using Strings to Name Hash Keys?

I'm working through a book called "Head First Programming," and there's a particular part where I'm confused as to why they're doing this.
There doesn't appear to be any reasoning for it, nor any explanation anywhere in the text.
The issue in question is in using multiple-assignment to assign split data from a string into a hash (which doesn't make sense as to why they're using a hash, if you ask me, but that's a separate issue). Here's the example code:
line = "101;Johnny 'wave-boy' Jones;USA;8.32;Fish;21"
s = {}
(s['id'], s['name'], s['country'], s['average'], s['board'], s['age']) = line.split(";")
I understand that this will take the string line and split it up into each named part, but I don't understand why what I think are keys are being named by using a string, when just a few pages prior, they were named like any other variable, without single quotes.
The purpose of the individual parts is to be searched based on an individual element and then printed on screen. For example, being able to search by ID number and then return the entire thing.
The language in question is Python, if that makes any difference. This is rather confusing for me, since I'm trying to learn this stuff on my own.
My personal best guess is that it doesn't make any difference and that it was personal preference on part of the authors, but it bewilders me that they would suddenly change form like that without it having any meaning, and further bothers me that they don't explain it.
EDIT: So I tried printing the id key both with and without single quotes around the name, and it worked perfectly fine, either way. Therefore, I'd have to assume it's a matter of personal preference, but I still would like some info from someone who actually knows what they're doing as to whether it actually makes a difference, in the long run.
EDIT 2: Apparently, it doesn't make any sense as to how my Python interpreter is actually working with what I've given it, so I made a screen capture of it working https://www.youtube.com/watch?v=52GQJEeSwUA

I don't understand why what I think are keys are being named by using a string, when just a few pages prior, they were named like any other variable, without single quotes
The answer is right there. If there's no quote, mydict[s], then s is a variable, and you look up the key in the dict based on what the value of s is.
If it's a string, then you look up literally that key.
So, in your example s[name] won't work as that would try to access the variable name, which is probably not set.
EDIT: So I tried printing the id key both with and without single
quotes around the name, and it worked perfectly fine, either way.
That's just pure luck... There's a built-in function called id:
>>> id
<built-in function id>
Try another name, and you'll see that it won't work.

Actually, as it turns out, for dictionaries (Python's term for hashes) there is a semantic difference between having the quotes there and not.
For example:
s = {}
s['test'] = 1
s['othertest'] = 2
defines a dictionary called s with two keys, 'test' and 'othertest.' However, if I tried to do this instead:
s = {}
s[test] = 1
I'd get a NameError exception, because this would be looking for an undefined variable called test whose value would be used as the key.
If, then, I were to type this into the Python interpreter:
>>> s = {}
>>> s['test'] = 1
>>> s['othertest'] = 2
>>> test = 'othertest'
>>> print s[test]
2
>>> print s['test']
1
you'll see that using test as a key with no quotes uses the value of that variable to look up the associated entry in the dictionary s.
Edit: Now, the REALLY interesting question is why using s[id] gave you what you expected. The keyword "id" is actually a built-in function in Python that gives you a unique id for an object passed as its argument. What in the world the Python interpreter is doing with the expression s[id] is a total mystery to me.
Edit 2: Watching the OP's Youtube video, it's clear that he's staying consistent when assigning and reading the hash about using id or 'id', so there's no issue with the function id as a hash key somehow magically lining up with 'id' as a hash key. That had me kind of worried for a while.

BioPython Pubmed Eutils url?

I'm trying to run some queries against Pubmed's Eutils service. If I run them on the website I get a certain number of records returned, in this case 13126 (link to pubmed).
A while ago I bodged together a python script to build a query to do much the same thing, and the resultant url returns the same number of hits (link to Eutils result).
Of course, not having any formal programming background, it was all a bit cludgy, so I'm trying to do the same thing using Biopython. I think the following code should do the same thing, but it returns a greater number of hits, 23303.
from Bio import Entrez
Entrez.email = "A.N.Other#example.com"
handle = Entrez.esearch(db="pubmed", term="stem+cell[All Fields]",datetype="pdat", mindate="2012", maxdate="2012")
record = Entrez.read(handle)
print(record["Count"])
I'm fairly sure it's just down to some subtlety in how the url is being generated, but I can't work out how to see what url is being generated by Biopython. Can anyone give me some pointers?
Thanks!
EDIT:
It's something to do with how the url is being generated, as I can get back the original number of hits by modifying the code to include double quotes around the search term, thus:
handle = Entrez.esearch(db='pubmed', term='"stem+cell"[ALL]', datetype='pdat', mindate='2012', maxdate='2012')
I'm still interested in knowing what url is being generated by Biopython as it'll help me work out how i have to structure the search term for when i want to do more complicated searches.

handle = Entrez.esearch(db="pubmed", term="stem+cell[All Fields]",datetype="pdat", mindate="2012", maxdate="2012")
print(handle.url)

You've solved this already (Entrez likes explicit double quoting round combined search terms), but currently the URL generated is not exposed via the API. The simplest trick would be to edit the Bio/Entrez/__init__.py file to add a print statement inside the _open function.
Update: Recent versions of Biopython now save the URL as an attribute of the returned handle, i.e. in this example try doing print(handle.url)