Day 6: Modules, Standard Library Suggested reading: Learning Python - - PowerPoint PPT Presentation

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Day 6: Modules, Standard Library Suggested reading: Learning Python - - PowerPoint PPT Presentation

Oct 11, 2022 223 likes •607 views

Computer Sciences 368 Scripting for CHTC Day 6: Modules, Standard Library Suggested reading: Learning Python (4th Ed.) Ch.21: Modules: The Big Picture Ch.22: Module Coding Basics http://docs.python.org/release/2.4.3/modindex.html 2012 Fall

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Cartwright 2012 Fall

Computer Sciences 368 Scripting for CHTC

Day 6: Modules, Standard Library

Suggested reading: Learning Python (4th Ed.) Ch.21: Modules: The Big Picture Ch.22: Module Coding Basics

http://docs.python.org/release/2.4.3/modindex.html

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Turn In Homework

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Homework Review

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Modules

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Python Module = .py File

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Why Write a Module?

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  • Maximize code reuse /

Minimize code redundancy

  • Organize code clearly (group related definitions)
  • Make testable units of code
  • Share data among separate script parts

(Does this list look familiar?)

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Importing a Module

  • 1. Looks up or else creates module object
  • 2. Assigns object to module_name
  • 3. Runs all top-level code in module!
  • 4. Objects are bound to names in module namespace:

– variables (via =) – functions (via def) – classes (via class) – other modules (via import)

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import module_name

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Accessing Module Parts

  • Same as accessing parts of an object
  • Because a module is an object, which is a namespace

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module_name.attribute import math f = 42 def circum(mult): d = 2 * f * mult return d * math.pi foo.py: import foo print foo.math.pi foo.f += 2 x = foo.circum(2) bar.py:

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Sample Module I

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_c2f_ratio = 5.0 / 9.0 # "private"-ish _f2c_ratio = 9.0 / 5.0 # "private"-ish def convert_c2f(deg_f): return (deg_f – 32.0) * _c2f_ratio def convert_f2c(deg_c): return (deg_c * _f2c_ratio) + 32.0 import temp_convert f = 70.0 c = temp_convert.convert_f2c(f) print "%.1f F = %.1f C" % (f, c)

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Sample Module II

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import csv datafile = 'results.csv' def load(): results = [] r = csv.reader(open(datafile, 'rb')) for row in reader: results.append(row) return results def write(data): # ...

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Standard Library

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Built-In Functions

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Review … and Some New Friends

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bool float int long str - dir help chr hex oct ord - len range - id type abs max min pow round sum - raw_input chr(97) => 'a'

  • rd('a') => 97

max(1, 2, 3, 4, 5) => 5 round(2.5) => 3.0 sum(range(1, 101)) => 5050 2 is (1 + 1) => True id(2), id(1 + 1) => (437788320, 437788320)

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Sorting

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list.sort(cmp, key, reverse) # all opt. names = ['Tim', 'Alain', 'scot', 'mat'] def lcmp(x, y): return cmp(x.lower(), y.lower()) names.sort() names.sort(cmp=lcmp) names.sort(key=str.lower, reverse=True) new_list = sorted(list, cmp, key, reverse)

Sort a list object in place: Sort any iterable object and make new list object:

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Transforming

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map(function, iterable, ...) >>> map(chr, range(65, 91)) ['A', 'B', 'C', …, 'Y', 'Z'] >>> map(str.capitalize, ('tim', 'mAt', …)) ['Tim', 'Mat', …] def mult(x, y): return x * y a = (2, 3, 6, 4, 8) b = (12, 8, 4, 6, 3) twentyfour = map(mult, a, b)

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Filtering

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filter(function, iterable) >>> t = ('Hi!', '42', '4.0', '-1', '1001') >>> filter(str.isdigit, t) ('42', '1001') def large(t): return t[1] > 100.0 p = {'cn': 1339.7, 'ph': 94.0, 'dk': 5.6, 'us': 312.5, 'in': 1210.2, 'ki': 0.1} big = dict(filter(large, p.items()))

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Numbers

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math

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pi e - ceil floor fmod fabs cos sin tan - degrees radians exp factorial log log10 pow sqrt 2 * math.pi => 6.283185307179586 math.log(math.e) => 1.0 math.ceil(2.5) => 3.0 math.floor(2.5) => 2.0 math.cos(1.0) => 0.5403023058681398 math.degrees(0.54) => 30.939720937064457 math.sqrt(90.0) => 9.486832980505138

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decimal

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  • Does exact decimal floating point math
  • Has pros and cons compared to regular floats
  • Very useful for fixed-decimal math (e.g., finance)

>>> 0.1 + 0.1 + 0.1 - 0.3 5.551115123125783e-17 >>> import decimal >>> Decimal('0.1') + Decimal('0.1') + \ ... Decimal('0.1') - Decimal('0.3') Decimal('0.0') >>> print Decimal('0.0') 0.0

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random

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random uniform gauss normalvariate … randint choice shuffle sample - seed random.random() => 0.26510474670383377 random.random() => 0.09321673054441892 random.normalvariate(100, 10) => 95.3900… random.randint(1, 100) => 42 x = range(1, 6) random.shuffle(x) x => [2, 4, 1, 5, 3] random.choice(['A', 'B', 'C', 'D']) => 'A'

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Dates and Times

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time

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time - localtime gmtime asctime strftime - mktime strptime >>> time.time() 1319402100.752616 >>> time.localtime()

time.struct_time(tm_year=2011, tm_mon=10, tm_mday=23, tm_hour=15, tm_min=35, tm_sec=20, tm_wday=6, tm_yday=296, tm_isdst=1)

>>> time.asctime() 'Sun Oct 23 15:36:51 2011' >>> time.strftime('%d %B %Y - %H:%M') '23 October 2011 - 15:36'

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datetime

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  • Complex set of classes for date/time calculations
  • Extra code required to handle timezones correctly

from datetime import datetime, timedelta start = datetime.now() wait = timedelta(weeks=1, hours=8) then = start + wait print then.strftime('%m/%d @ %H:%M')

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calendar

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  • Mostly for printing fixed-width text calendars
  • Does a few other date calculations

>>> calendar.prmonth(2011, 11) November 2011 Mo Tu We Th Fr Sa Su 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

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Files

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csv

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file = open(csv_file, 'rb') reader = csv.reader(file) for row in reader: # row is list, 1 item/CSV field Tim Cartwright,4265,2-4002,"CHTC, OSG" Alain Roy,4261,5-5736,"CHTC, OSG" Greg Thain,4279,0-0031,CHTC

  • Used by Excel and others
  • Wildly inconsistent, non-standardized format
  • Hard to parse yourself, use the module instead
  • Can offer hints as to particular CSV format
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fnmatch

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fnmatch fnmatchcase filter file = raw_input('Enter filename: ') if not fnmatch.fnmatch(file, '*.html'): print 'Please enter an HTML file!' files = os.listdir('.') for file in fnmatch.filter(files, '*.py'): print 'Python file:', file

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glob

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  • Acts like shell wildcards
  • Uses fnmatch for implementation

for pth in glob.glob('travel/201?/*.csv'): print 'Recent travel table:', pth file = open(pth, 'rb') reader = csv.reader(file) # ...

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The System

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sys

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stdin stdout stderr - platform version getrefcount - modules - path prefix getsizeof float_info long_info maxint

plus lots more!

sys.platform => 'linux2' sys.version_info => (2, 4, 3, 'final', 0) sys.getrefcount(2) => 33 sys.getrefcount(1234) => 2 sys.maxint => 2147483647 len(sys.modules) => 30

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  • s

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chdir getcwd - readlink symlink unlink chmod chown stat - remove rename makedirs mkdir rmdir - listdir walk

plus lots more!

for t in os.walk(path): # t = (dirname, subdirs, files) for f in t[2]: if fnmatch.fnmatch(f, '*.py'): print 'Py:', os.path.join(t[0], f)

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  • s.path

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abspath realpath basename dirname join split exists isdir isfile islink getatime getctime getmtime getsize dir = 'wibble/wobble' file = raw_input('File? ') path = os.path.join(dir, file) if os.path.exists(path) and \

  • s.path.getsize(path) > 0:

print 'Path:', os.path.abspath(path) print 'Size:', os.path.getsize(path) print 'Mod:', os.path.getmtime(path)

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shutil

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copy copy2 copytree copymode copystat - move - rmtree shutil.copy('a.txt', 'b.txt') shutil.copy2('a.txt', 'a.txt.backup') shutil.move('dir1/a.txt', 'dir2/a.txt') shutil.rmtree('be/really/careful')

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Last 2 Slides!

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Other Scripting Languages

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  • Modules

– Code organization systems are fairly universal – Syntax, semantics, etc., vary considerably!

  • Standard Library

– Yes! – Part of what makes a language (not) suitable for a task – Huge variation

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Homework

  • Write source files to multiple target directories
  • May modify file contents each time
  • Use lots of standard Python modules/functions!!!
  • [Optional:] Write a simple module for some of sol’n
  • Be sure to label your printout

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#!/usr/bin/env python """Homework for CS 368-4 (2012 Fall) Assigned on Day 06, 2012-11-08 Written by <Your Name> """