Otherwise, the installation aborts without any warning. You can configure many interpreters and choose the desire one for each of your project.
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Many of the Python packages require python-dev Python development tools to install and build. There are two versions of pip : pip2 for Python 2 and pip3 for Python 3. The pip executable could be symlinked to either pip2 or pip3. The apt-get install may not install the latest pip version.
You could upgrade pip using pip itself, as follows:. The most important feature of pip is to manage a full list of packages at specific version numbers, so as to synchronize two environments such as the development and production environments. Furthermore, via the so-called virtual environment to be described next , each Python application can maintain its own list and versions of packages.
A Python "Virtual Environment" is a dedicated directory which contains everything that a Python application needed to run the application in an isolated environment. It includes its own Python interpreter, its own pip and all the pip -installed packages. Via virtual environments, you can test and run different Python applications with different Python versions and packages.
You can also easily synchronize the development Python environment and the production Python environment. To install virtualenv via pip 2 for Python 2 or pip3 for Python 3 :. Suppose that we start a new Python project in the development environment, and would like the project to run under specific versions of Python Interpreter and packages, which is isolated from the system environment and can be duplicated to the production environment.
We can create a virtual environment for this project, which is basically a directory keeping its own Python Interpreter and packages isolated from the system packages and can be duplicated in another environment. Take note that all commands issued under a virtual environment run under the Python of the virtual environment. Similarly, pip issued under a virtual environment installs the package inside the virtual environment.
The extensions include wrappers for creating and deleting virtual environments and otherwise managing your development work flow, making it easier to work on more than one project at a time without introducing conflicts in their dependencies. Conda Package Management System Anaconda uses the open-source conda package management system for managing packages and their dependencies install and update , and the environment.
Jupyter Notebook is a successor to the earlier iPython Notebook, started in The default start-up directory is probably not your desired working directory. To change the start-up directory, shutdown the previous app Press Ctrl-C twice at the console. Launch the Anaconda Prompt from the Start menu Windows.
Change directory to your desired start-up directory and run " jupyter notebook ". To create a new notebook for Python, click "New" and select "Python". A new notebook is opened in a new tab. It is saved as " Untitled. You can check its contents later after performing some operations. Jupyter's code is organized in fragments called cells.
Type " print 'Hello World! The label changes from In to In.
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The number 1 indicates when the cell was executed on the kernel. This tutorial uses Python 3, because it more semantically correct and supports newer features. For example, one difference between Python 2 and 3 is the print statement. In Python 2, the "print" statement is not a function, and therefore it is invoked without parentheses.
However, in Python 3, it is a function, and must be invoked with parentheses. Python uses indentation for blocks, instead of curly braces. Both tabs and spaces are supported, but the standard indentation requires standard Python code to use four spaces. The formula for h and the dependence on the variables are clearer now. The last line printed the value of h :. The variable h in this example refers to a specific number and not a symbolic formula. As a result, if you change v or g , the value of h won't change, even if we originally set h by a formula involving v and g.
To see what we mean, try typing the following:. The point here is that h stays the same, even though v has been changed. To update h to reflect the new v , we need to repeat the formula:. Until we write another assignment statement with h on the left hand side, the value of h does not change.
Assignment statements can be chained together to update a variable without creating a new variable. For example, on my birthday, my age is increased by one year. The following commands would be good for marking my birthday. We have been using Python interactively for these first quick answers and examples.
Interactive shell sessions are nice for trying a couple of commands in a row.
But if you need to chain together a sequence of several commands, as in the last exercise, it is much more efficient to save them to a file and use IDLE to run the file. A set of Python commands in a file is called a script.
Like a movie script for an actor, the Python script tells the Python interpreter what to do and in what order to do it. First, we'll introduce comments , which are lines of text that are ignored by the Python interpreter but that are included to help explain your code to others and to remind yourself what your code is intended to do. Good code writing requires good comments. Comments in Python start with a sign. Any text following the sign is ignored by the interpreter. For example, if you cut and paste the following command into the Python shell, the text after the this print statement will not be printed.
Notice that the color highlighting in the code block makes comments appear grayed out. This is the type convention followed by the wiki software we are using; some people find the comments hard to read as a result. Activity 8: Now we will save some commands to a file and run the file as a Python script. Your session might look something like this, with the file window on the left and the shell on the right.
In the file window on the left, we've entered the commands and you can see that IDLE has colored the text using its syntax highlighting.
The Python Interpreter and IDLE — CSC Intro to Programming documentation
It does this in both the shell and file windows. The script consists of the set of commands you have already run interactively. We have added comments that start with to help document the code. When you selected Run Module or typed F5 , several things happened.
Run Module or F5 is a command that asks IDLE to translate compile the code into a form the computer can understand, load the translated code into the computer memory, and run the commands in the script one at a time in the order they are written. This clears out all previous settings and memory usage.
It then runs each separate line in your script as a command. That is, the script executes all the command sequentially, in the order that they are written. It skips every comment line in the script. This means that is now waiting for further instructions. You can now go ahead and type additional commands interactively. Activity 9: Create and run another script for practice. Mistakes, Bugs, Errors, Warnings: It is sad but true that most of your time in programming will be spent debugging finding and fixing coding errors. Strategies for debugging are covered here in the Python Reference, but this is a good point to say something about IDLE's debugging hints.
You will find that when a code contains errors that are obvious, IDLE will try to inform you that it sees the problem and will try to identify where the problem might be. For example, in the following, the first line introduces a syntax error and the second tries to print the value of a variable that has not been defined. Activity Do the following. You can explore these as you get more comfortable with Python, but IDLE is sufficient for our purposes. This section started out with an introduction on starting IDLE for Python and running programs from it. Using IDLE, inputting and using the shell was also demonstrated.
By now you should surely be comfortable with both IDLE and the python shell and the basic operations they can be used for.
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