Natural Language Processing with Python

Summary

• Python’s assignment and parameter passing use object references; e.g., if a is a list and we assign b = a, then any operation on a will modify b, and vice versa.

• The is operation tests whether two objects are identical internal objects, whereas == tests whether two objects are equivalent. This distinction parallels the type-token distinction.

• Strings, lists, and tuples are different kinds of sequence object, supporting common operations such as indexing, slicing, len(), sorted(), and membership testing using in.

• We can write text to a file by opening the file for writing

  ofile = open('output.txt', 'w'

  then adding content to the file ofile.write("Monty Python"), and finally closing the file ofile.close().

• A declarative programming style usually produces more compact, readable code; manually incremented loop variables are usually unnecessary. When a sequence must be enumerated, use enumerate().

• Functions are an essential programming abstraction: key concepts to understand are parameter passing, variable scope, and docstrings.

• A function serves as a namespace: names defined inside a function are not visible outside that function, unless those names are declared to be global.

• Modules permit logically related material to be localized in a file. A module serves as a namespace: names defined in a module—such as variables and functions—are not visible to other modules, unless those names are imported.

• Dynamic programming is an algorithm design technique used widely in NLP that stores the results of previous computations in order to avoid unnecessary recomputation.