Python for perl programmers
Fernando Pineda 140.636 Similari es between Perl & Python
• Like perl, python is: – A ‘scrip ng’ language but also a general purpose language. – Interpreted – Comments start with ‘#’ – Mul ple programming paradigms are supported • impera ve • object-based • func onal – Dynamically typed – Large package repositories (CPAN, PyPI) Packages & repositories
• Comprehensive Perl • Python Package Index Archive Network (CPAN) (PyPI) • ~175K packages in CPAN • ~90K packages in PyPI • cpan • easy_install • cpanm • pip • use • import Differences between perl & python
• Python (like C and Java) is strongly typed • Python code blocks delimited via indenta on rather than code blocks • Built in interac ve-shell (perl has e.g. Devel::REPL) • In python EVERYTHING is an object Built-in Types Perl Python
• int,long • scalar • float,complex • array • string* • hash • list • tuple* • set • frozenset* * immutable python objects • dict h ps://docs.python.org/2/library/types.html • ...etc. Code blocks
perl python foreach my $x in (1..9) { for x in range (1,10) print “$x\n”; print(x) } versions, programs & scripts perl script python script perl --version python --version
#!/usr/bin/env perl #!/usr/bin/env python
... perl statements ... ‘’’ python statements ... raw input()
#!/usr/bin/env python
# raw)input() returns a string object age = raw_input("What is your age? ")
# print() prints the string print (“your age: “+ age )
# type() returns a type ‘type’ # print() prints the type print(type(age)) Anonymous func ons
perl python my $f= sub { f = lambda x: my $x = shift; return 2*x return 2*$x; } print(f(2))
print $func_ref->(2) my $f= sub { 2*shift} f= lambda x: 2*x print $func->(2) print (f(2)) In python everything is an object
• type()shows the type of an object • dir() shows the methods in an object
type(“hello”)
dir(“hello”)
“hello”.__add__(“ world”)
type(9/8)
print(9/8) Crea ng your own objects perl python Package MyClass; class MyClass: def __init__(self): sub new { self.x = None return bless{x=>undef} }
$obj = MyClass->new(); obj = MyClass perl with Moo Package MyClass; use Moo; has x => {is => ‘rw’} Map perl (map)
my @items= 1..9; @squared = map {$_**2} @items python (map) items= range(1,10) squared = list(map(lambda x: x**2, items)) python (list comprehension)
list= range(1,10) squared = [x**2 for x in list] Reduce perl (reduce)
use List::Util (‘reduce’); my @items= 1..9; my $sum= reduce { $a + $b } @items; python (reduce) from functions import reduce items= range(1,10) sum = reduce(lambda x,y: x+y, items)) Trouble with versions
• Python 2.x vs Python 3.x – v.3 released in Dec. 2008 – Not backward compa ble with Python 2.x – Many projects s ll in Python 2.x – PyPI has 25,948 v.5 packages ported to v.6(out of 90839) • Perl 5.x vs Perl 6.x – v.6 released in Dec. 2015 (announced in 2000) – Not backward compa ble with Perl 5.x – CPAN has 173,63 v.5 packages but does not yet support v.6 packages Ra onalizing language issues
• Prepend to Python 2.x modules
from __future__ import absolute_import from __future__ import division from __future__ import print_function from __future__ import unicode_literals ...etc.
print 8/7 # with and with ‘division module’ • Prepend to Perl 2.x scripts and modules
use Modern::Perl; use Moo; # simplifies object creation/usage Addi onal material
• h ps://docs.python.org • h ps://pypi.python.org • h p://modernperlbooks.com/books/ modern_perl_2016