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Python Script - easy examples of lots of basics

Here's a Python script which is pretty imperfect, but shows a whole lot of the basic facilities of the language in use - a sort of "you can do it this way" crib sheet for newcomers. Written during last week's course, with delegates making suggestions as I went along - so if you think the code looks like it was designed by a committee of eleven ....

The overall objective is to read in a web server access log file and report the elepase time in days and hours from the first to the last record .... I will add comments which we did NOT add on the day!


# Bring in regular expression and time handling code from the Python
# distribution which is NOT loaded as standard every time you run an
# individual Pyton program. Use import to keep each in their own
# namespace rather than from which would pollute the top level.
import re
import time
  
# Set up some standards - incoming file name, and the pattern to look
# for when hunting for a date and time stamp in a record
fname = "access_log.xyz"
linematch=re.compile(r'(\d{2})/(\w{3})/(\d{4}):(\d{2}):(\d{2}):')
months=["Jan","Feb","Mar","Apr","May","Jun",
  "Jul","Aug","Sep","Oct","Nov","Dec"]
  
# Read in the whole file and keep the SECOND and last lines only
# Line counts starts at zero, by the way - but in our data file the
# first line is a header record that we want to ignore.
# Enhancement note - do NOT use readlines if the source file is huge
info = open(fname,"r").readlines()
lines = [info[1],info[-1]]
print lines
  
# Define a function that extracts a timestamp using a
# rerular expression, and returns seconds from 1.1.70
def getsecs(matcher,stri):
  dt = matcher.findall(stri)
  elapsed = list(dt[0])
# index saves a loop to look for the number for the month!
# Months grabbed from outside so that different month names
# can be used if you're not working in English!
  elapsed[1] = months.index(elapsed[1])+1
  elt = time.mktime((int(elapsed[2]), int(elapsed[1]),
    int(elapsed[0]), int(elapsed[3]),
    int(elapsed[4]), 0,0,0,0));
  return elt
  
# Bit messy this bit - get elapsed time via a loop
# (I was trying to be too clever with the code!
tato = 0
for sample in lines:
  tat = getsecs(linematch,sample)
  print tat
  tat = tat - tato
  tato = tat
print tat
  
# And get the days and hours ...
el = int(tat)
days = el / (3600*24)
elx = el - days * 3600 * 24
hours = elx / 3600
print days,hours


Running that ...

grahamellis$ python daterange
['seaweed - - [15/Jul/1998:08:32:38 -0400]
"GET / HTTP/1.0" 200 1476\n',
'sealion - - [02/Feb/1999:11:54:03 +0000]
"GET /perlman/READMEs/README.threads HTTP/1.1" 200 10787\n']
900491520.0
917956440.0
17464920.0
202 3
grahamellis$

(written 2007-12-08, updated 2007-12-12)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Y105 - Python - Functions, Modules and Packages
  [4724] From and Import in Python - where is the module loaded from? - (2016-11-06)
  [4722] Embedding more complex code into a named block - (2016-11-04)
  [4719] Nesting decorators - (2016-11-02)
  [4662] Recursion in Python - the classic example - (2016-03-07)
  [4645] What are callbacks? Why use them? An example in Python - (2016-02-11)
  [4448] What is the difference between a function and a method? - (2015-03-04)
  [4441] Reading command line parameters in Python - (2015-02-23)
  [4410] A good example of recursion - a real use in Python - (2015-02-01)
  [4407] Python - even named code blocks are objects - (2015-01-28)
  [4361] Multiple yields and no loops in a Python generator? - (2014-12-22)
  [4212] Python functions - an introduction to how they work - (2013-11-16)
  [4161] Python varables - checking existance, and call by name or by value? - (2013-08-27)
  [4029] Exception, Lambda, Generator, Slice, Dict - examples in one Python program - (2013-03-04)
  [3945] vargs in Python - how to call a method with unknown number of parameters - (2012-12-06)
  [3931] Optional positional and named parameters in Python - (2012-11-23)
  [3885] Default local - a good choice by the author of Python - (2012-10-08)
  [3852] Static variables in Python? - (2012-08-29)
  [3766] Python timing - when to use a list, and when to use a generator - (2012-06-16)
  [3695] Functions are first class variables in Lua and Python - (2012-04-13)
  [3662] Finding all the unique lines in a file, using Python or Perl - (2012-03-20)
  [3474] Python Packages - groupings of modules. An introduction - (2011-10-11)
  [3472] Static variables in functions - and better ways using objects - (2011-10-10)
  [3464] Passing optional and named parameters to python methods - (2011-10-04)
  [3459] Catching the fishes first? - (2011-09-27)
  [3280] Passing parameters to Python functions - the options you have - (2011-05-07)
  [3159] Returning multiple values from a function call in various languages - a comparison - (2011-02-06)
  [2998] Using an exception to initialise a static variable in a Python function / method - (2010-10-13)
  [2994] Python - some common questions answered in code examples - (2010-10-10)
  [2929] Passing a variable number of parameters in to a function / method - (2010-08-20)
  [2878] Program for reliability and efficiency - do not duplicate, but rather share and re-use - (2010-07-19)
  [2766] Optional and named parameters to Python functions/methods - (2010-05-15)
  [2718] Python - access to variables in the outer scope - (2010-04-12)
  [2520] Global and Enable - two misused words! - (2009-11-30)
  [2506] Good example of recursion in Python - analyse an RSS feed - (2009-11-18)
  [2481] Sample code with errors in it on our web site - (2009-10-29)
  [2440] Optional parameters to Python functions - (2009-10-07)
  [2439] Multiple returns from a function in Python - (2009-10-06)
  [2011] Conversion of OSI grid references to Eastings and Northings - (2009-01-28)
  [1879] Dynamic code - Python - (2008-11-11)
  [1871] Optional and named parameters in Python - (2008-11-05)
  [1870] What to do with a huge crop of apples - (2008-11-04)
  [1869] Anonymous functions (lambdas) and map in Python - (2008-11-04)
  [1790] Sharing variables with functions, but keeping them local too - Python - (2008-09-09)
  [1784] Global - Tcl, PHP, Python - (2008-09-03)
  [1202] Returning multiple values from a function (Perl, PHP, Python) - (2007-05-24)
  [1163] A better alternative to cutting and pasting code - (2007-04-26)
  [1134] Function / method parameters with * and ** in Python - (2007-04-04)
  [959] It's the 1st, not the 1nd 1rd or 1th. - (2006-12-01)
  [949] Sludge off the mountain, and Python and PHP - (2006-11-27)
  [913] Python - A list of methods - (2006-11-03)
  [912] Recursion in Python - (2006-11-02)
  [900] Python - function v method - (2006-10-20)
  [821] Dynamic functions and names - Python - (2006-08-03)
  [775] Do not duplicate your code - (2006-06-23)
  [749] Cottage industry or production line data handling methods - (2006-06-07)
  [745] Python modules. The distribution, The Cheese Shop and the Vaults of Parnassus. - (2006-06-05)
  [668] Python - block insets help with documentation - (2006-04-04)
  [561] Python's Generator functions - (2006-01-11)
  [418] Difference between import and from in Python - (2005-08-18)
  [386] What is a callback? - (2005-07-22)
  [340] Code and code maintainance efficiency - (2005-06-08)
  [308] Call by name v call by value - (2005-05-11)
  [303] Lambdas in Python - (2005-05-06)
  [294] Python generator functions, lambdas, and iterators - (2005-04-28)
  [105] Distance Learning - (2004-10-31)
  [96] Variable Scope - (2004-10-22)


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