This is an old one. In Java, HashSet delegates all its functions to HashMap.
What goes on under the covers of a HashSet<T> is:
- A member variable, map, of type HashMap<T, Object> is maintained.
- All operations on HashSet is delegated to a corresponding operation on HashMap - add(), remove(), contains(), etc.
- A dummy object
add(T objOfTypeT)
Invokes put(objOfTypeT, dummy object)
remove(T objOfTypeT)
Invokes HashMap's remove(objOfTypeT)
size()
returns map's size
contains(T objOfTypeT)
returns map.containsKey(objOfTypeT)
iterator()
returns map's keySet's iterator
I am new to python. I am using python 2.7.5.
I was working on writing a screen scrapper for one of my projects. I am using scrapy framework for screen scrapping.
After setting up and testing my spider, I wanted to test how it could be called from another Python script. Till this point I had been testing using scrapy's commands.
I looked up online to find an example to call scrapy from another Python script. Scrapy, it seems, uses a network framework called twisted. Twisted was not installed in my machine. So, I proceeded to do a sudo apt-get install python-twisted in my command prompt. That did not seem to work.
I created a sample twisted script and attempted to run that. This would help in testing if Python really recognizes Twisted Obviously, that failed.
So, after a bit of looking around, I stumbled upon this. Python packages needs to be installed from tar files. So, download a tar file, un-tar it. This should create a source directory which is supposed to have a file called setup.py. To install the package, run python setup.py install
This is exactly what I did. I downloaded tar of Twisted from here. Then un-tar'ed it using tar xjf Twisted-13.1.0.tar.bz2 which created a folder Twisted-13.1.0. Then changed directory into Twisted-13.1.0 using cd Twisted-13.1.0. Finally, python setup.py install. This gave an error. Twisted required another package called zope.interface.
I downloaded tar of zope.interface from here and then did the above steps first for zop.interface so zope gets installed. Then proceeded to Twisted-13.1.0 folder to do a python setup.py install in that folder.
So, in general, if you need to install a package in Python, get the tar file and use python install feature on setup.py file of the tar.
