python

Python/PyTango/IPython in a Nutshell
Version March 5, 2025
by
Thorsten Kracht

Contents
Introduction
Miscellaneous
- Python2 to Python3
- Hello world
- Command line arguments
- Executing a string of commands from the command line
- The name of the executing script
- Indentation using XEmacs
Variables
- Type
- Scope, local, global, builtin
- Numbers
  - Operators
- Strings
- Lists
- Dictionaries
- Tuples
  - Tuples to lists
- Sets
- Special global variables
Modules and Packages
- Some Statements on Modules and Packages
- Importing modules
- Demo: Importing modules from packages and sub-packages
- Circular imports
- The toplevel name space, __builtins__
- Injecting a variable into the name space of a module
Classes
- General remarks
- Class definition
  - Class variables
- Multiple constructors
- Inspect the members of a class
- The class of an instance
- Import classes from a module
- Inheritance
- Exceptions are classes
- Default attributes handler
- delattr(), getattr(), setattr()
- The @staticmethod decorator
- The @classmethod decorator
- The property function
- The @property decorator
Control Statements
- If
  - Operators
  - Truth
- Loops
  - Break an outer loop
  - Loop over a list in pairs
Input/Output
- Print
- Internal write
- sys.stdin.readline()
- Press <return> to continue
- sys.stdout.write
- File I/O
- touch
Built-in Functions
- callable()
- chr(), ord()
- dir()
- exec()
- eval()
- delattr(), getattr(), setattr()
  - use getattr() to make callbacks
- globals() (example from 00-start.py)
- hasattr()
- id()
- int(), float(), str()
- int(), round()
- issubclass()
- iter()
- lambda (closure)
- map, filter
- locals()
- map()
- range()
- sort(), sorted()
- type(), isinstance()
- yield
Useful modules
- argparse
  - A trivial example, consuming one command line argument
  - Another trivial example
  - nargs
  - DoAll.py
- atexit
- commands
  - getoutput(), capturing shell command output, hostname
- cProfile
- datetime (also rfc2822)
- distutils
- doty to datetime
- glob, unix style pathname pattern expansion
  - glob, sorting file names wrt. time
  - glob, sorting file names
  - glob, find latest file in a directory
- importlib
- importlib, reload
- inspect (all members of a class)
- math
  - math.fabs
  - math.radians, math.degrees
  - math.sin
- matplotlib
  - General remarks
  - Simple vs. OO API
  - Blocking mode
  - Non-blocking, from IPython, debugging
  - Create a png, useful for web applications
  - Subplots
  - Plotting from the MacroServer
  - Scan simulation
  - fioPlotter
- multiprocessing
- psutil, python system and process utilities
  - find process by name
  - system utilization
- pyqtgraph
  - General remarks
  - Scan simulation
  - fioPlotter
  - Mouse moves and clicks
  - Plotting from MacroServer
- numpy
  - array
  - ndarray, basic slicing
  - ndarray, select rows and columns
  - ndarray, ellipsis [...]
  - arange
  - linspace
  - ones
  - zeros
- os
  - os.access()
  - os.chdir()
  - os.chmod()
  - os.environ
  - os.getcwd()
  - os.getenv()
  - os.getpid()
  - os.isatty()
  - os.kill()
  - os.listdir() (all files in a directory)
  - os.mkdir()
  - os.path.abspath(), current files directory path
  - os.path.basename()
  - os.path.dirname()
  - os.path.exists()
  - os.path.getmtime()
  - os.path.getsize()
  - os.path.isdir()
  - os.path.isExecutable()
  - os.path.isfile()
  - os.popen(), capturing shell command output
  - os.popen(), ps ax, MacroServer/haspp09
  - os.popen(), with time-out
  - os.remove(), os.rmdir()
  - os.rename() (mv)
  - os.system(), execute a shell command, sensing the return-state
  - os.system(), calling ping
  - os.walk(), traverse dirs and sub-dirs
- platform
- pprint
- random, seed(), setstate(), getstate()
- shelve, persistent dictionary
- shlex, split preserving quoted substrings
- shutil, copy files
  - copy
- signal
  - signal
- socket
  - gethostname()
  - gethostbyaddr()
- string
  - atoi()
  - find()
  - lower(), upper()
  - partition, rpartition()
  - replace()
  - split(), join()
  - strip(), strip(), lstrip()
- subprocess, capturing shell command output
- swig
- sys
  - argv
  - exitfunc
  - getframe(), traceback
  - path (PYTHONPATH)
  - stdin.readline()
  - Python version, version_info
- threads
- time
  - ctime()
  - localtime(), date and time
  - strftime(), formatted date-time string
  - doty(), day-of-the-year
  - sleep(), usleep()
  - time()
- traceback
  - traceback.format_exc
  - traceback.print_tb
- zeromq
  - A client
  - A mirror
Functions
- Definition
- Argument passing
  - Convert a list to a dictionary then expand
- Returning a list
- Modifying a list from within a function
Exceptions
- Catching exceptions
- Traceback Information
- Raising an exception
- User defined exception
- Tango exceptions
- AttributeError
- Catching a time-out
Details
- Reference counts
- The identity of variables/objects
- 'del x' vs. 'x = None'
- Trigger garbage collection
- Modify a list from within a function
IPython
- General remarks
  - TAB-Completion
  - Command history
- Configuration
- Magic
- Commands
Tango I/O Speed
- Reading the Position Attribute
- Reading the Counts Attribute
- Precise Cycle Times for Reading the Position and Counts
- Position reading while the motor is moving
Examples
- VmExecutors
- VcExecutors
- Other Tango examples
- Tango database
- I/O
- Miscellaneous
- Taurus application, process events
- QtGui, QtCore
Appendix
- Pattern
Bibliography
Index
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