Using print statements only to debug

Question

I have been coding a lot in Python of late  And I have been working with data that I haven t worked with before  using formulae never seen before and dealing with huge files   All this made me write a lot of print statements to verify if it s all going right and identify the points of failure  But  generally  outputting so much information is not a good practice  How do I use the print statements only when I want to debug and let them be skipped when I don t want them to be printed

User · Answer

I don t know about others  but I was used to define a  global constant   DEBUG  and then a global function  debug msg   that would print msg only if DEBUG    True   Then I write my debug statements like   debug  My value   d    value       then I pick up unit testing and never did this again

User · Answer

A better way to debug the code is  by using module clrprint It prints a color full output only when pass parameter debug True from clrprint import   clrprint  ERROR    information clr   r   y    debug True

User · Answer

A simple way to do this is to call a logging function   DEBUG   True  def log s       if DEBUG          print s  log  hello world     Then you can change the value of DEBUG and run your code with or without logging   The standard logging module has a more elaborate mechanism for this

User · Answer

Use the logging built-in library module instead of printing   You create a Logger object  say logger   and then after that  whenever you insert a debug print  you just put   logger debug  Some string     You can use logger setLevel at the start of the program to set the output level  If you set it to DEBUG  it will print all the debugs  Set it to INFO or higher and immediately all of the debugs will disappear   You can also use it to log more serious things  at different levels  INFO  WARNING and ERROR

User · Answer

First off  I will second the nomination of python s logging framework   Be a little careful about how you use it  however   Specifically  let the logging framework expand your variables  don t do it yourself   For instance  instead of   logging debug  datastructure   r    complex dict structure    make sure you do   logging debug  datastructure   r   complex dict structure    because while they look similar  the first version incurs the repr   cost even if it s disabled   The second version avoid this   Similarly  if you roll your own  I d suggest something like   def debug stdout sfunc       print sfunc     debug   debug stdout   called via   debug lambda   datastructure   r    complex dict structure    which will  again  avoid the overhead if you disable it by doing   def debug noop  args    kwargs       pass  debug   debug noop   The overhead of computing those strings probably doesn t matter unless they re either 1  expensive to compute or 2  the debug statement is in the middle of  say  an n 3 loop or something   Not that I would know anything about that

User · Answer

The logging module has everything you could want  It may seem excessive at first  but only use the parts you need  I d recommend using logging basicConfig to toggle the logging level to stderr and the simple log methods  debug  info  warning  error and critical   import logging  sys logging basicConfig stream sys stderr  level logging DEBUG  logging debug  A debug message    logging info  We processed  d records   len processed records

[python] Using print statements only to debug

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