Partial Function Application

Partial Function Application in Python

A look under the hood of popular Python repositories on GitHub

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What is Partial Function Application?

1  def powern(x, n):    
2      return x**n
3  
4  print(power(2,3))  # Outputs 8

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What is Partial Function Application?

1  from functools import partial
2  
3  power2 = partial(powern, x=2)
4  
5  print(power2(3))  # Outputs 8

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Popular repositories on Github

• Using GitHub Search Api
• More than 100 stars
• Conda
• Pip

• bidict

  Conda

  Dry run of Conda commands using partial application

$ conda rename -n oldname newname

$ conda rename -n oldname newname -d

  Dry run action: clone /path-to/oldname,/path-to/newname
  Dry run action: rm_rf /path-to/oldname

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Conda

1   def clone_and_remove() 
2    actions = (
3        partial(install.clone, source, destination),
4        partial(rm_rf, source)
5    )
6    
7    for func in actions:
8        if args.dry_run:
9            print(f"{DRY_RUN_PREFIX} {func.func.__name__} {','.join(func.args)}")
10       else:
11           func()

Source Code

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Pip

Command Options

$ pip install --help

1  class Option:
2      def process(self, opt, value, values, parser):
3          #--------
4           elif action == "help":
5                parser.print_help()
6                parser.exit()
7          #--------

Source Code

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Pip

Pre-configuration of options for commands without initialisation

1  help_ = partial(
2      Option,
3      "-h",
4      "--help",
5      dest="help",
6      action="help",
7      help="Show help.",
8  )

Source Code

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Bidict

• bidict provides a bidirectional mapping, allowing lookups in both directions.
• Useful for scenarios like encoding/decoding, where both forward and reverse mappings are needed.

1  b["four"] = 4
2  print(b.inv[4])  # Outputs "four"

Source Code

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Bidict - putall

b = bidict({1: 'one', 2: 'two'})

# Multiple updates - all or nothing
b.putall([
    (3, 'three'),  # Would succeed
    (1, 'uno'),    # Will fail (key exists)
    (4, 'four')    # Won't be attempted
])

# Result: b still equals {1: 'one', 2: 'two'}

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Bidict - putall

1  def _update():
2      unwrites = []
3      for key, val in iteritems(arg, **kw):
4          try:
5              dedup_result = self._dedup(key, val, on_dup)
6          except DuplicationError:
7              if rbof:
8                  while unwrites:
9                      for unwriteop in unwrites.pop():
10                         unwriteop()
11                 raise
12          if dedup_result is None:
13              continue
14          write, unwrite = prep_write(key, val, *dedup_result, save_unwrite=rbof)
15          for writeop in write:
16              writeop()
17          if rbof:
18              append_unwrite(unwrite)

Source Code

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Bidict - Inside PrepWrite

1  def _prep_write(self):
2      fwdm_set, invm_set = fwdm.__setitem__, invm.__setitem__
3      write = [
4          partial(fwdm_set, newkey, newval),
5          partial(invm_set, newval, newkey),
6      ]
7      unwrite = [
8          partial(fwdm_del, newkey),
9          partial(invm_del, newval),
10     ]
11     return write, unwrite

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Who am I?

amin-mousavi.dev Senior Software Engineer @ CBA