Standard Library

Dr Andy Evans

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Core libraries

• Scripts, by default only import sys (various system services/functions) and builtins (built-in functions, exceptions and special objects like None and False).
• The Python shell doesn't import sys, and builtins is hidden away as __builtins__.

Built in functions

• https://docs.python.org/3/library/functions.html

Python Standard Library

• Documentation and tutorials:
  https://docs.python.org/3/py-modindex.html
  https://docs.python.org/3/library/index.html
  https://docs.python.org/3/tutorial/stdlib.html
  
• Most give useful recipes for how to do major jobs you're likely to want to do.

Useful libraries: text

• difflib - for comparing text documents; can for example generate a webpages detailing the differences.
  https://docs.python.org/3/library/difflib.html
• Unicodedata - for dealing with complex character sets. See also "Fluent Python"
  https://docs.python.org/3/library/unicodedata.html
• regex
  https://docs.python.org/3/library/re.html

Collections

https://docs.python.org/3/library/collections.html
# Tally occurrences of words in a list
c = Counter()
for word in ['red', 'blue', 'red', 'green', 'blue', 'blue']:
    c[word] += 1
print(c)

<Counter({'blue': 3, 'red': 2, 'green': 1})>

• Find the ten most common words in Hamlet:
  import re
words = re.findall(r'\w+',
open('hamlet.txt').read().lower())
Counter(words).most_common(5)

[('the', 1143), ('and', 966), ('to', 762), ('of', 669), ('i', 631)]
https://docs.python.org/3/library/collections.html#collections.Counter

Useful libraries: binary data

• Binary
  https://docs.python.org/3/library/binary.html
• See especially struct:
  https://docs.python.org/3/library/struct.html

Useful libraries: maths

• math
  https://docs.python.org/3/library/math.html
• decimal - Does for floating points what ints do; makes them exact
  https://docs.python.org/3/library/decimal.html
• fractions - Rational numbers (For dealing with numbers as fractions
  https://docs.python.org/3/library/fractions.html

Statistics

• https://docs.python.org/3/library/statistics.html

Random selection

• Random library includes functions for:
  • Selecting a random choice
  • Shuffling lists
  • Sampling a list randomly
  • Generating different probability distributions for sampling.

Auditing random numbers

• Often we want to generate a repeatable sequence of random numbers so we can rerun models or analyses with random numbers, but repeatably.
• https://docs.python.org/3/library/random.html#bookkeeping-functions
• Normally uses os time, but can be forced to a seed.

Useful libraries: lists/arrays

• bisect - Array bisection algorithm (efficient large sorted arrays for finding stuff)
  https://docs.python.org/3/library/bisect.html

Useful libraries: TkInter

• https://docs.python.org/3/library/tk.html
• Used for Graphical User Interfaces (windows etc.)
• Wrapper for a library called Tk (GUI components) and its manipulation languages Tcl.
• See also:
  wxPython: Native looking applications:
  https://www.wxpython.org/
  (Not in Anaconda)

Turtle

• https://docs.python.org/3/library/turtle.html
• For drawing shapes.
• TKInter will allow you to load and display images, but there are additional external libraries better set up for this, including Pillow:
  http://python-pillow.org/

Useful libraries: talking to the outside world

• Serial ports
  https://docs.python.org/3/faq/library.html#how-do-i-access-the-serial-rs232-port
• argparse - Parser for command-line options, arguments and sub-commands
  https://docs.python.org/3/library/argparse.html
• datetime
  https://docs.python.org/3/library/datetime.html

Databases

• DB-API
  https://wiki.python.org/moin/DatabaseProgramming
• dbm - Interfaces to Unix "databases"
  https://docs.python.org/3/library/dbm.html
  Simple database
• sqlite3 - DB-API 2.0 interface for SQLite databases
  https://docs.python.org/3/library/sqlite3.html
  Used as small databases inside, for example, Firefox.