• In Python2.X print is a statement not a function.
  • Very intutive but not very powerful.
>>> answer = 42
>>> print "The answer is: " + str(answer)
The answer is: 42
  • In Python 3.X print is a function which gives it more control on how to print stuff.
  • You can import print funtion into python 2.7.X using the statement from future import print_function
  • I would recommend using print as a function even in Python2.X, for one your code will be more compatiable with Python3.X and also print function gives you more control on the output.
>>> from __future__ import print_function       # This internally sets a flag that lets interpreter enable print function
>>> answer = 42
>>> print('The answer is: '+str(42))
The answer is: 42
  • Print as a funtion can take arguments which provide more control on how you ptint stuff.
print(value1, ..., sep=' ', end='\n', file=sys.stdout, flush=False)
#
#    file: a file-like object (stream); defaults to the current sys.stdout.
#    sep:  string inserted between values, default a space.
#    end:  string appended after the last value, default a newline.
#
  • With the end argument you can choose what is appended as the last value.
# Building a simple NOP sled for memory exploits
# Only one of the output works for a NOP sled. Which one? Why?(Out of this workshop context though)
>>>
>>> print('\x90'*30)
������������������������������
>>> 
>>> print('\x90'*30, end='')
������������������������������>>> 
>>>
  • By redefining the keyword parameter file we can send the output into a different stream e.g. to a file or stderr
>>> fh = open("data.txt","w")
>>> print("42 is the answer, but what is the question?", file=fh) 
>>> fh.close()      # we see no ouput  to console after print because it's directed into the file fh

C-Style format strings

  • The nearest thing to c-style printf equivalent in python.
  • '%s %s' % ('one', 'two')

format string 

>>> port_number = 139
>>> 
>>> host = '10.5.0.6'
>>> 
>>> print "Port num: %d is open on Host: %s"%(port_number, host)
Port num: 139 is open on Host: 10.5.0.6


For more on format string modulo: http://www.python-course.eu/python3_formatted_output.php

Pythonic style - string format method.

  • Python has awesome string formatters to produce beautifully formatted output.

  • The “fields to be replaced” are surrounded by curly braces {}.  '{} {}'.format('one', 'two')

>>> print "[+] Port num: {} on host {} is open.".format(port_number, hostname)

Placeholders

  • Python string format method supports placeholders and an explicit positional index.  {1} {0}'.format('one', 'two')
  • A positional parameter of the format method can be accessed by placing the index of the parameter after the opening brace, e.g. {0} accesses the first parameter.

format string


- Keywords can be used to index parameters as well.(Named placeholders)

>>> "Art: {a:5d},  Price: {p:8.2f}".format(a=453, p=59.058)
'Art:   453,  Price:    59.06'
>>>

Padding and aligning strings

By default values are formatted to take up only as many characters as needed to represent the content. It is however also possible to define that a value should be padded to a specific length.

  • We can precede the formatting with a “<” (left justify) or “>” (right justify)
>>> '{:>10}'.format('test')                             # right align
'      test'
>>>
>>> "{0:<20s} {1:6.2f}".format('Spam & Eggs:', 6.99)    # left align
'Spam & Eggs:           6.99'
>>>
>>>'{:^10}'.format('test')                          #center align
'   test   '

>>> print "\nThe webserver is at IP: {0:<20} -- Port {1:>20}\n".format('192.172.10.21','8080')

The webserver is at IP: 192.172.10.21        -- Port                 8080
  • Choose your character for padding. '{:_<10}'.format('test')
>>> '{:_<10}'.format('test')
'test______'


Further reading on string format method https://pyformat.info/

sys.stdout.write()

This could be used to write to standard output or consoles when print doesn’t seem to work.

>>> pack = '\x90\x32\x67\x70'
>>> sys.stdout.write(pack)
�2gp>>>