gitter-badger / python-varname Goto Github PK

Dark magics about variable names in python

Installation

pip install python-varname

Features

• Fetching variable names from inside the function/class call
• Fetching variable names directly (added in v0.1.2)
• A value wrapper to store the variable name that a value is assigned to (added in v0.1.1)
• Detecting next immediate attribute name (added in v0.1.4)
• Shortcut for collections.namedtuple (added in v0.1.6)
• Injecting __varname__ to objects (added in v0.1.7)

Credits

Thanks goes to these awesome people/projects:

@alexmojaki

executing

Usage

Retrieving the variable names from inside a function call/class instantiation

• From insdie a function call

  from varname import varname
  def function():
      return varname()
  
  func = function()
  # func == 'func'

• varname calls being buried deeply

  def function():
      # I know that at which stack this will be called
      return varname(caller=3)
  
  def function1():
      return function()
  
  def function2():
      return function1()
  
  func = function2()
  # func == 'func'

• Retrieving instance name of a class

  class Klass:
      def __init__(self):
          self.id = varname()
  
      def copy(self):
          # also able to fetch inside a member call
          return varname()
  
  k = Klass()
  # k.id == 'k'
  
  k2 = k.copy()
  # k2 == 'k2'

• Some unusual use

  func = [function()]
  # func == ['func']
  
  func = [function(), function()]
  # func == ['func', 'func']
  
  func = function(), function()
  # func = ('func', 'func')
  
  func = func1 = function()
  # func == func1 == 'func'
  # a warning will be printed
  # since you may not want func1 to be 'func'
  
  x = func(y = func())
  # x == 'x'
  
  # get part of the name
  func_abc = function()[-3:]
  # func_abc == 'abc'
  
  # function alias supported now
  function2 = function
  func = function2()
  # func == 'func'
  
  # Since v0.1.3
  # We can ask varname to raise exceptions
  # if it fails to detect the variable name
  
  from varname import VarnameRetrievingError
  def get_name():
      try:
          # if raise_exc is False
          # "var_<index>" will be returned
          return varname(raise_exc=True)
      except VarnameRetrieveingError:
          return None
  
  a.b = get_name() # None

Value wrapper

from varname import Wrapper

foo = Wrapper(True)
# foo.name == 'foo'
# foo.value == True
bar = Wrapper(False)
# bar.name == 'bar'
# bar.value == False

def values_to_dict(*args):
    return {val.name: val.value for val in args}

mydict = values_to_dict(foo, bar)
# {'foo': True, 'bar': False}

Getting variable names directly

from varname import varname, nameof

a = 1
aname = nameof(a)
# aname == 'a

b = 2
aname, bname = nameof(a, b)
# aname == 'a', bname == 'b'

def func():
    return varname() + '_suffix'

f = func()
# f == 'f_suffix'
fname = nameof(f)
# fname == 'f'

Detecting next immediate attribute name

from varname import will
class AwesomeClass:
    def __init__(self):
        self.will = None

    def permit(self):
        self.will = will()
        if self.will == 'do':
            # let self handle do
            return self
        raise AttributeError('Should do something with AwesomeClass object')

    def do(self):
        if self.will != 'do':
            raise AttributeError("You don't have permission to do")
        return 'I am doing!'

awesome = AwesomeClass()
awesome.do() # AttributeError: You don't have permission to do
awesome.permit() # AttributeError: Should do something with AwesomeClass object
awesome.permit().do() == 'I am doing!'

Shortcut for collections.namedtuple

# instead of
from collections import namedtuple
Name = namedtuple('Name', ['first', 'last'])

# we can do:
from varname import namedtuple
Name = namedtuple(['first', 'last'])

Injecting __varname__

from varname import inject

class MyList(list):
    pass

a = inject(MyList())
b = inject(MyList())

a.__varname__ == 'a'
b.__varname__ == 'b'

a == b

# other methods not affected
a.append(1)
b.append(1)
a == b

Limitations

• Working in ipython REPL but not in standard python console
• You have to know at which stack the function/class will be called (caller's depth)
• Not working with reticulate from R since it cuts stacks to the most recent one.
• nameof cannot be used in statements in pytest (supported in v0.2.0)

  -a = 1
  +assert nameof(a) == 'a'
  -# Retrieving failure.
  -# The right way:
  -aname = nameof(a)
  -assert aname == 'a'