A friend of mine asked how to implement a python function to truncate a string to the first n words. Easy!
def truncate_string(mystring, numberofwords): return ' '.join(mystring.split()[:numberofwords]) |
An example of use:
>>> sample_string = "hello world this is a string" >>> print truncate_string(sample_string,2) hello world |
Some days ago a friend of mine who is learning python asked for my help. He was experimenting issues with spanish special characters (such as tildes -á,é,í,ó,ú- and -ñ-) when retrieving data from a MySQL database.
When I looked at the code, I saw he was connecting to MySQL using MySQLdb connect function as in:
import MySQLdb as mdb con = mdb.connect(host='localhost',user='myuser',passwd='mypassword',db='mydatabase') |
And he was astonished because I was able to solve his problems just by changing that to:
import MySQLdb as mdb con = mdb.connect(host='localhost',user='myuser',passwd='mypassword',db='mydatabase', charset='utf8', use_unicode=False) |
So don’t underestimate the power of official documentation and please, RTFM!
We updated our CentOS machines and when we restarted our Apache servers, and tried to access the sites, a “500 Internal Server Error” was being shown.
We noticed some ugly shit in Apache error.log:
ImportError: cannot import name urandom [Tue Nov 27 11:45:17 2012] [error] make_obcallback: Python path being used "['/usr/lib64/python2.4/site-packages/setuptools-0.6c5-py2.4.egg', '/usr/lib64/python2.4/site-packages/rdflib-2.4.0-py2.4-linux-x86_64.egg', '/usr/lib64/python2.4/site-packages/cx_Oracle-5.0-py2.4-linux-x86_64.egg', '/usr/lib64/python2.4/site-packages/MySQL_python-1.2.2-py2.4-linux-x86_64.egg', '/usr/lib/python2.4/site-packages/pylint-0.18.1-py2.4.egg', '/usr/lib/python2.4/site-packages/logilab_astng-0.19.1-py2.4.egg', '/usr/lib/python2.4/site-packages/logilab_common-0.44.0-py2.4.egg', '/usr/lib/python2.4/site-packages/pysnmp_apps-0.2.9a-py2.4.egg', '/usr/lib/python2.4/site-packages/pysnmp-4.1.13a-py2.4.egg', '/usr/lib/python2.4/site-packages/pyasn1-0.0.11a-py2.4.egg', '/usr/lib64/python24.zip', '/usr/lib64/python2.4', '/usr/lib64/python2.4/plat-linux2', '/usr/lib64/python2.4/lib-tk', '/usr/lib64/python2.4/lib-dynload', '/usr/lib64/python2.4/site-packages', '/usr/lib64/python2.4/site-packages/Numeric', '/usr/lib64/python2.4/site-packages/gtk-2.0', '/usr/lib/python2.4/site-packages']". [Tue Nov 27 11:45:17 2012] [error] get_interpreter: no interpreter callback found. |
To fix this, you must check the following:
[root@aneto ~]# rpm -q mod_python mod_python-3.2.8-3.1 [root@aneto ~]# rpm -q httpd httpd-2.2.3-65.el5_8.3 [root@aneto ~]# rpm -q python python-2.4.3-46.el5_8.2 |
If the output is like the one above, then run:
[root@aneto ~]# yum downgrade python python-libs |
And then restart Apache. Issues should be now fixed.
Python makes some tasks easy. For instance, removing duplicate elements from a list can be done like:
>>> myList = [1, 2, 3, 3, 2, 2, 4, 5, 5] >>> myList [1, 2, 3, 3, 2, 2, 4, 5, 5] >>> myList = list(set(myList)) >>> myList [1, 2, 3, 4, 5] >>> |
Cheers to python! 
If you try something like this in python:
a = os.system("find / -name myfile.ext") print a # the output for find will be printed, but 'a' will store the exit code of the find command |
So, how do you save the output of os.system to a variable? Use the subprocess module and proceed like:
>>> import subprocess >>> command = "find / -name myfile.ext" >>> proc = subprocess.Popen(command,stdout=subprocess.PIPE,shell=True) >>> (out, err) = proc.communicate() >>> outwithoutreturn = out.rstrip('\n') >>> print out ./myfile.ext >>> print outwithoutreturn >>> ./mifile.ext >>> |
Some time ago I posted some cds invenio mysql useful queries. Some people wrote some days ago asking wether I could put this into a function. Here you are 
List all deleted records which belong(ed) to collection ‘colname’ (tested with Invenio 0.99.x)
def listDeletedFromCollname(colname, coltag='980__c'): from invenio.dbquery import run_sql query = """ SELECT distinct bibrec_bib98x.id_bibrec FROM bib98x, bibrec_bib98x WHERE bib98x.tag='%s' AND bib98x.value = '%s' AND bib98x.id = bibrec_bib98x.id_bibxxx AND bibrec_bib98x.id_bibrec IN (SELECT DISTINCT bibrec_bib98x.id_bibrec FROM bibrec_bib98x, bib98x WHERE bibrec_bib98x.id_bibxxx=bib98x.id AND bib98x.tag = '980__c' AND bib98x.value = 'DELETED') """ %(coltag,colname) res = run_sql(query) deletedlist = [] for i in res: deletedlist.append(i[0]) return deletedlist |
And it is used like:
# list deleted records from a collecion defined by the query '980__c:FH' a = listDeletedFromCollname('FH') print a # if I have my collection defined in another way, for instance using this query: '980__a:TAZ' a = listDeletedFromCollname('TAZ','980__a') print a |
In a similar fashion we can list the ones that have NOT been deleted, as in:
def listNotDeletedFromCollname(colname, coltag='980__c'): from invenio.dbquery import run_sql query = """ SELECT distinct bibrec_bib98x.id_bibrec FROM bib98x, bibrec_bib98x WHERE bib98x.tag='%s' AND bib98x.value = '%s' AND bib98x.id = bibrec_bib98x.id_bibxxx AND bibrec_bib98x.id_bibrec NOT IN (SELECT DISTINCT bibrec_bib98x.id_bibrec FROM bibrec_bib98x, bib98x WHERE bibrec_bib98x.id_bibxxx=bib98x.id AND bib98x.tag = '980__c' AND bib98x.value = 'DELETED') """ %(coltag,colname) res = run_sql(query) notdeletedlist = [] for i in res: notdeletedlist.append(i[0]) return deletedlist |
Hope it’s useful
I learned a python trick that saved me a lot of time when using the interpreter. Just wanted to share it with you.
>>> import rlcompleter, readline >>> readline.parse_and_bind("tab:complete") |
With the above lines you’ll have a unix-like autocomplete for functions. For instance, if you type
>>> import os >>> os. |
And then you press “TAB” the list of OS module functions will show up. Ain’t it AWESOME? :>
A friend of mine asked yesterday: how do I get the mod_python version that my site is running?
Answer is quite easy!
>>> import mod_python >>> print mod_python.version 3.3.1 |
If you are getting a message like this:
>>> import cx_Oracle Traceback (most recent call last): File "<stdin>", line 1, in ? ImportError: libclntsh.so.11.1: wrong ELF class: ELFCLASS32 |
It means you are having issues with ELF (Executable and Linkable Format)
How to solve em?
First, locate the path to libclntsh.so.11.1 (usually in /usr):
[root@zaguan importaFHdesdeRoble]# find / -name "libclntsh.so.11.1" /usr/lib/oracle/11.1/client64/lib/libclntsh.so.11.1 /usr/lib64/libclntsh.so.11.1 |
Note the presence of two files. Lets check wether they are for 32bits or 64bits:
[root@zaguan importaFHdesdeRoble]# file /usr/lib/oracle/11.1/client64/lib/libclntsh.so.11.1 /usr/lib/oracle/11.1/client64/lib/libclntsh.so.11.1: ELF 64-bit LSB shared object, AMD x86-64, version 1 (SYSV), not stripped [root@zaguan importaFHdesdeRoble]# file /usr/lib64/libclntsh.so /usr/lib64/libclntsh.so: ELF 32-bit LSB shared object, Intel 80386, version 1 (SYSV), not stripped |
If your system is 64 bits (check it out with uname -a) you should be using the ELF 64-bit LSB shared object.
So, you can just:
mv /usr/lib64/libclntsh.so.11.1 /usr/lib64/libclntsh.so.11.1__32bits cp /usr/lib/oracle/11.1/client64/lib/libclntsh.so.11.1 /usr/lib64/libclntsh.so.11.1 |
And now, you will be able to import Oracle library from python:
# python Python 2.4.3 (#1, Apr 14 2011, 20:41:59) [GCC 4.1.2 20080704 (Red Hat 4.1.2-50)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> import cx_Oracle >>> |
Or, if you want to do it “the right way”. Put this in a script.sh file and alter
#!/bin/bash PATH=$PATH:$HOME/bin ORACLE_HOME=/usr/lib/oracle/11.1/client64 LD_LIBRARY_PATH=/usr/lib/oracle/11.1/client64/lib export ORACLE_HOME export LD_LIBRARY_PATH export PATH # ALTER HERE with the path to python and the file which has the python code to connect to Oracle salida=`/usr/bin/python ./pythoncodefile.py` |