Added readme file

README.md

@@ -1 +1,153 @@
-# merry
+# merry
+
+[![Build Status](https://travis-ci.org/miguelgrinberg/merry.svg?branch=master)](https://travis-ci.org/miguelgrinberg/merry)
+
+Decorator based error handling for Python
+
+## Installation
+
+Merry is installed with pip:
+
+    $ pip install merry
+
+## Getting Started
+
+The purpose of merry is to help you move error handling code away from your
+application logic. Take, for example, this function, which embeds error
+handling code:
+
+```python
+def write_to_file(filename, data):
+    try:
+        with open(filename, 'w') as f:
+            f.write(data)
+    except IOError:
+        print('Error: can't write to file')
+    except Exception as e:
+        print('Unexpected error: ' + str(e))
+
+write_to_file('some_file', 'some_data')
+```
+
+Even with this simple example, you can see how the indentation forced by the
+try/except block makes the code much harder to read and visually follow.
+
+Merry allows you to move exception handlers to external functions, so that
+they don't interfere with the application logic:
+
+```python
+from merry import Merry
+
+merry = Merry()
+
+@merry._except(IOError)
+def ioerror():
+    print('Error: can't write to file')
+
+@merry._except(Exception)
+def catch_all(e):
+    print('Unexpected error: ' + str(e)
+
+@merry._try
+def write_to_file(filename, data):
+    with open(filename, 'w') as f:
+        f.write(data)
+
+write_to_file('some_file', 'some_data')
+```
+
+While in this example there is more total lines of code after merry is used,
+the key benefit is that the application logic, which is in the `write_to_file`
+function, is now completely clean of try/except statements. The exception
+handlers become auxiliary functions that can be moved to a separate module so
+that they stay out of the way.
+
+The decorated exception handlers can take zero or one argument. If they take
+an argument, then merry sends the exception object.
+
+## The `else` and `finally` clauses
+
+For cases where a more complex try/except block is required, there are also
+decorators available for `else` and `finally`:
+
+```python
+@merry._else
+def else_clause():
+    print('No exceptions where raised!')
+
+@merry._finally
+def finally_clause():
+    print('Clean up time!')
+```
+
+## Passing context to error handlers
+
+In many cases, exception handlers need to have access to application state to
+do their work. When using merry, the `merry.g` object can be used to set
+application state that needs to be accessible to error handlers:
+
+```python
+@merry._except(Exception)
+def catch_all():
+    db = getattr(merry.g, 'database', None)
+    if db is not None and is_database_open(db):
+        close_database(db)
+    print('Unexpected error, quitting')
+    sys.exit(1)
+
+@merry._try
+def app_logic():
+    db = open_database()
+    merry.g.database = db  # save it in the error context just in case
+    # do database stuff here
+```
+
+## Debug mode
+
+When working with debuggers, it is a good idea to let all exceptions reach the
+top of the stack, so that the debugger handles them. With merry, if you enable
+debug mode all exceptions bubble all the way up:
+
+```python
+merry = Merry(debug=True)
+```
+
+But when working in debug mode, there might be certain exceptions that are
+expected to trigger and do not need to bubble up. For this reason, the debug
+mode can be overriden by individual error handlers:
+
+```python
+@merry._except(IOError, debug=False)
+def ioerror():
+    print('Error: can't write to file')
+```
+
+## Logging
+
+Conversely, when an application is running in production mode, it is desired
+that all errors are suppressed and instead they are sent to a log. Merry
+creates a logger on which it writes all the exceptions it handles, include
+their backtraces. This logger is a standard instance of the Python standard
+library logging class.
+
+The logger instance is called `'merry'` by default, and can be referenced as
+`merry.logger`. If desired, merry can hook up to a logger owned by the
+application:
+
+```python
+custom_logger = logging.getLogger('my_logger')
+custom_logger.setLevel(logging.INFO)
+merry = Merry(logger_name='my_logger')
+```
+
+By default, the logger created by merry does not have any handlers attached,
+so caught exceptions will not be printed anywhere. If you want exceptions
+to be printed to the console, you can add a handler that writes to stderr:
+
+```python
+merry = Merry()
+merry.logger.addHandler(logging.StreamHandler(sys.stderr))
+```
+
+The log level and format can be adjusted as well. See the documentation on the
+logging module for more information on how to do this.