python_fast_track_june_17.md

Python Fast Track

Speaker: Rick Copeland

3rd session

String processing and regular expressionss

• String interpolation
• String methods
• String templates
• Regular expression

String interpolation

'My favorite number is %s' % 42
'My favorite number is %(num)d' % {'num': 42}
import math
'The value of pi %.3f' % math.pi
'The value of pi %-20d' % math.pi  # padding with spaces
'The value of pi %.20d' % math.pi  # padding with zeros
'Value of pi {0}'.format(math.pi)

String methods

split()

text = '''hello world there'''
words = text.split()

join()

'-'.join(words)

strip(): remove front and back spaces

lstrip(): remove only front spaces

rstrip(): remove only back spaces

title(): Captialize the initial of each word

isdigit(): is a number?

index('substr'): the index of the matching substr

find('substr', index=0): find the substr in str, starting from index

rfind('substr', index=0): find the substr in str backwardly, starting from index

str.center(num): 'hello'.center(50)

text.lower(),

text.upper(),

text.swapcase(),

String template

import string
tmpl = string.Template('''
	Dear $name, 
''')
tmpl.substitute(dictionary)
tmpl.safe_substitute(dictionary)

Side notes:

import StringIO: makes a text like a file.

from collections import defaultdict: make a default value for dict.

from collections import Counter: counting

Regular Expressions

import re

re.match('quick', text)

match = re.match('.*quick', text)

match.groups()

match = re.match('[a-z]+', text) # longest 

match = re.match('[a-z]+?', text)# shortest

m = re.search('brown (?P<animal>[a-z]+) jumped', text)

m.groups()

m.groupdict()

re_time= re.compile('\\d{2}:\\d{2}:\\d{2}')

re_time.match('01:02:03').groups()

re_time = re.compile(r'\d{2}:\d{2}:\d{2}')

re_time = re.compile(r'''
stuff # comments
(\d{2}) # another comments
''', re.VERBOSE)

re.search('quick.brown', text, re.DOTALL | re.VERBOSE) #. matches anything but a newline

re.finditer('\w+', text)

re.sub()

re.split() # split text with pattern

Packages and Modules

Package Layout

• Build your own modules
• __init__.py to represents it is a module
• if __name__ == '__main__ ' # like int main() ...

Tips:

1. When import subpackage, it will also import the parent package.
2. When import parent package, it is not guaranteed to to import its sub-modules
3. When import as module, it will cache it to make it faster to import it again.

More modules at here and there.

Python Module of the Week