Python snippets

pause.md

• Implementing pause

import os
os.system('read -s -n 1 -p "Press any key to continue...\n"')

snippets.md

---

• Natural (human) sort (REF.)

  convert = lambda text: int(text) if text.isdigit() else text
  foo = ["f" + str(x) for x in range(20)]
  foo.sort()
  print foo   # ['f0', 'f1', 'f10', 'f11', 'f12', 'f13', 'f14', 'f15', 'f16', 'f17', 'f18', 'f19', 'f2', 'f3', 'f4', 'f5', 'f6', 'f7', 'f8', 'f9']
  foo.sort(key=lambda x : [convert(c) for c in re.split('(\d+)', x)])
  print foo   # ['f0', 'f1', 'f2', 'f3', 'f4', 'f5', 'f6', 'f7', 'f8', 'f9', 'f10', 'f11', 'f12', 'f13', 'f14', 'f15', 'f16', 'f17', 'f18', 'f19']

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• Unicode to ASCII At times when we have certain unicode characters that Python is not able to convert to ASCII, it throws this exception:

  UnicodeEncodeError: 'ascii' codec can't encode character u'\uXXXX' in position 8: ordinal not in range(128)

  Where XXXX is some unicode value For e.g., if we have a unicode char 'en dash' (&#x2013) instead of the hyphen (&#x2d) (REF) for Unicode dash chars, the unicode value for en dash is U+2013 and for hyphen is U+002D

  >>> hyphen = u'\u002d'
  >>> en_dash = u'\u2013'
  >>> 
  >>> print hyphen
  -
  >>> print en_dash
  –
  >>> print str(hyphen)
  -
  >>> print str(en_dash)
  Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  UnicodeEncodeError: 'ascii' codec can't encode character u'\u2013' in position 0: ordinal not in range(128)

  To overcome this, we have a lib - unidecode:

  >>> import unidecode
  >>> unidecode.unidecode_expect_ascii(en_dash)
  '-'
  >>>
  

---

• Nicely print Exceptions (more readings here and here)

  import linecache
  import sys
  
  def PrintException():
    exc_type, exc_obj, tb = sys.exc_info()
    f = tb.tb_frame
    lineno = tb.tb_lineno
    filename = f.f_code.co_filename
    linecache.checkcache(filename)
    line = linecache.getline(filename, lineno, f.f_globals)
    print '{} IN ({}, LINE {} "{}"): {}'.format(exc_type.__name__, filename, lineno, line.strip(), exc_obj)
    
  try:
    print 1/0
  except:
    PrintException()
  
  # Output:
  # ZeroDivisionError IN (foo.py, LINE 14 "print 1/0"): integer division or modulo by zero

Python 3

import sys
import traceback

def PrintException():
    exc_type, exc_value, exc_traceback = sys.exc_info()
    formatted_exception = traceback.format_exception(
        etype=exc_type,
        value=exc_value,
        tb=exc_traceback
    )
    return "".join(formatted_exception)

---

• dict of dict of stuff (without getting a KeyError) (REF.)

  >>> from collections import defaultdict
  >>>
  >>> d1 = defaultdict(lambda: 0)
  >>> d2 = defaultdict(list)
  >>> d3 = defaultdict(lambda: defaultdict(list))
  >>> 
  >>> print d1[1]
  0
  >>> d1
  defaultdict(<function <lambda> at 0x6f9c73b18de8>, {1: 0})
  >>> 
  >>> d2['1'].append(1)
  >>> d2
  defaultdict(<type 'list'>, {'1': [1]})
  >>> 
  >>> d3['1']['2'].append(12)
  >>> d3
  defaultdict(<function <lambda> at 0x6f9c73ab27d0>, {'1': defaultdict(<type 'list'>, {'2': [12]})})

  But never forget: Errors should never pass silently.