Python: an introduction for PHP webdevelopers

PYTHON: AN
INTRODUCTION FOR
PHP DEVELOPERS

What will we talk about?
Some general information about Python

Some code - enough to be able to read and understand
python code

Some minimal practical examples of python code and that
based on things that I picked up @ Dx-Solutions.
Any questions ? Feel free to interrupt !

What is python ?
Python is a widely used general-
purpose, high-level programming
language.

Its design philosophy emphasises code
readability.

Python supports multiple programming
models, including object-oriented,
procedural and functional
programming.

Has a large and comprehensive
standard library.

Python can be run on many operating
systems and (embedded) platforms.

Things that rule
It’s easy, ﬂexible and powerful.
Good to have in your toolbox!

String handling is fantastic

A wide range of good third party
libraries (because it has a close
relationship with C)

It is extremely versatile (web, gui
apps, arduino yun, scripting …)

Great prototype language

It’s really fun

Things that can bite
Uses whitespace (tabs) to delimit
program blocks (personal
preference)

It isn’t the fastest language (but
projects like cython, pypy, …
counters that)

Python 3 is not backward
compatible unfortunately. In this
presentation we will focus on
Python 2.x.

Package management could be
better and isn’t that good like in
node.js or PHP

In Belgium
Not a lot of big players

Mobile Vikings

Belgacom BIC

GDF Suez

Belﬁus

…

Lot of misconceptions

(toy language, only for experiments, small startups, …)

Starting to get some traction in higher education (university of Gent,
Leuven, Antwerp)

Some web frameworks
https://github.com/vinta/awesome-python
BeautifulSoup

Work project: Ghelamco
CSV ﬁelds -> doctrine generator.
Really speeded up the process to
create entities.

SQL generator to automatically
generate dump queries

Tool to dump table column names
(for example to use in certain
queries)

RAW dump importer (that served
as a prototype for a PHP symfony
command)

To generate doctrine entity ﬁelds
… now imagine if you need to do that manually…
Average runtime: less than a second…

Personal project: WebGL baking tool
http://www.simplicity.be/improving-realism-in-webgl-scenes-by-using-texture-baking/

IDE
Python comes with a builtin IDE “Idle” which feels
a bit dated and isn’t that good

PHPStorm lovers will be glad to know that
jetbrains also has a python IDE called PyCharm

Community edition is free

But the web support isn’t in the free edition

But in reality every text editor will suﬃce

Running python
• Through the interactive python shell
$ python

Python 2.7.9 (default, Dec 19 2014, 06:00:59)

[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.56)] on
darwin

Type "help", "copyright", "credits" or "license" for more
information.

>>> print "hello world"

hello world

>>>

Running python
• By running a .py ﬁle
hello.py
print "hello world"
$ python hello.py

hello world
command

2 very handy methods
dir

list attributes and methods

help
shows builtin help

dir (example)
>>> dir("dx-solutions")
['__add__', '__class__', '__contains__', '__delattr__', '__doc__',
'__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__',
'__getnewargs__', '__getslice__', '__gt__', '__hash__', '__init__',
'__le__', '__len__', '__lt__', '__mod__', '__mul__', '__ne__',
'__new__', '__reduce__', '__reduce_ex__', '__repr__', '__rmod__',
'__rmul__', '__setattr__', '__sizeof__', '__str__',
'__subclasshook__', '_formatter_field_name_split',
'_formatter_parser', 'capitalize', 'center', 'count', 'decode',
'encode', 'endswith', 'expandtabs', 'find', 'format', 'index',
'isalnum', 'isalpha', 'isdigit', 'islower', 'isspace', 'istitle',
'isupper', 'join', 'ljust', 'lower', 'lstrip', 'partition',
'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit',
'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase',
'title', 'translate', 'upper', 'zfill']

help (example)
>>> help(“dx-solutions”.upper)
Help on built-in function upper:
upper(...)
S.upper() -> string
Return a copy of the string S converted to uppercase.
(END)

Comments
A comment in python start with a hash (#) symbol

No multiline comments

use multiple #

Comments (examples)
// hello world
/**
* hello
* world
**/
PHP
# hello world
# hello
# world
Python

Variables
Python is a dynamically typed language. So you
do not need to declare variables before using
them or declare their type (like PHP)

Every variable in Python is an object…

…that has an id

…that is of a certain standard data type

…that has a mutable or immutable value

Mutable vs immutable
Mutable: you can change an object without
changing its identity. So in other words when you
alter an object its id will be the same.

Immutable: you can not change an object without
changing its identity. So when you alter an object
its id will change!

Mutable vs immutable (examples)
>>> myval = "dxsolutions"
>>> id(myval)
4538483456
>>> myval = "dx-solutions"
>>> id(myval)
4538475888
Immutable
>>> mylist = []
>>> id(mylist)
4538197848
>>> mylist.append("hello")
>>> id(mylist)
4538197848
Mutable

Standard data types
Number

integer

ﬂoat

long

complex

String

List

Tuple

Dictionary

Variables declarations (examples)
$var_1 = 1; // Integer
$var_2 = 3.14; // Float
$var_3 = "hello"; // String
$var_4 = 'hello'; // String
PHP
var_1 = 1 # Integer
var_2 = 3.14 # Float
var_3 = "hello" # String
var_4 = 'hello' # String
var_1 = 'abc' # Is now a string
Python

Math operators
Arithmetic operators are the same as PHP
Notation Description
+ add
- subtract
* multiply

/ division
% modulo
** power operator*
* the ** operator is introduced in PHP 5.6

Assignment operators
= simple assignment
+= add and assign
-= subtract and assign

*= multiply and assign
/= divide and assign
%= modulo and assign
**= exponent and assign*
//= ﬂoor division and assign*
* not available in PHP

Comparison operators
== is equal*
!= not equal
<> not equal
> bigger than
< smaller than
>= bigger than or equal
<= smaller than or equal
* doesn’t have the === operator

Logical operators
and and
or or
not not

Chained comparisons
# chained
if 5 < x < 7:
print 6
# same as
if x > 5 and x < 7:
print 6

Strings (examples)
$var_1 = 'Thunderstruck';
$var_2 = "Ain't no sunshine";
$var_3 = 'Ain't no sunshine';
$var_3 = "this has
multiple
lines";
PHP
Python
var_1 = 'Thunderstruck'
var_2 = "Ain't no sunshine"
var_3 = 'Ain't no sunshine'
var_3 = """this has
multiple
lines"""

Print
print ('Thunderstruck');
echo 'Thunderstruck';
PHP
print ('Thunderstruck'); # python 3.x
print 'Thunderstruck'; # python 2.x
Python

String formatting (examples)
>>> "Hello %s %s" % ("Glenn", "De Backer")
'Hello Glenn De Backer'
C syntax
>>> "Hello {0}, {1}".format("Glenn", "De Backer")
'Hello Glenn, De Backer’
>>> "Hello {firstname}, {name}".format(firstname="Glenn",
name="De Backer")
'Hello Glenn, De Backer'
Advanced string formatting (PEP 3101) (PEP = Python Enhancement Proposals)

Slices
Strings are a sequence of characters

A subsequence of a sequence is called a slice

The operation that extracts a subsequence is called slicing
a[start:end] items start through end-1
a[start:] items start through the rest of the array
a[:end] items from the beginning through end-1

a[:] a copy of the whole array
a[start:end:step] start through not past end, by step

Slices
a[-1] # last item in the array
a[-2:] # last two items in the array
a[:-2] # everything except the last two items
FROM HTTP://WWW.NLTK.ORG/BOOK/CH03.HTML

None
None is the pythonic way of deﬁning NULL.

Evaluates to False

Is an object (NoneType)

Because it is an object, we cannot use it to check
if a variable exist.

None (example)
db_con = None
# Try to connect
try:
db_con = MysqlDB(db_host, db_user, db_password, db_database)
db_con = database.connect()
except DatabaseException:
pass
if db_con is None:
print('Could not connect')
else:
# do dbase stuff

Booleans
Simple same as in PHP but case sensitive!

True

False

1

0

Booleans (examples)
$a = True;
$b = FALSE;
if ($a === true) {
echo "Party!";
}
PHP
a = True
b = False
if a is True:
print “party"
if a == True:
print "party"
Python

Sequences
Diﬃcult to compare as PHP only has associative arrays
( hashmap )

List: is just a list of items

Tuples: are like lists but you cannot change their values.

months

blood types

…

Dictionary: hashmap / associative arrays

Also supports slices and slicing

List (example 1/2)
>>> mylist = []
>>> mylist.append(123)
>>> mylist.append('dxsolutions')
>>> mylist.append(2)
>>> print mylist
[123, ‘dxsolutions’, 2]
>>> mylist.sort()
>>> print mylist
[2, 123, ‘dxsolutions']
>>> mylist.reverse()
>>> print mylist
['dxsolutions', 123, 2]

List (example 2/2)
>>> mylist.pop()
2
>>> print mylist
['dxsolutions', 123]
>>> mylist.extend([1,2,3])
>>> print mylist
['dxsolutions', 123, 1, 2, 3]
>>> mylist.remove(2)
>>> print mylist
['dxsolutions', 123, 1, 3]

Tuples (example)
>>> days = (‘monday’,'tuesday','wednesday','thursday',
'friday','saterday','sunday')
>>> days[2]
'wednesday'
>>> days[2:]
('wednesday', 'thursday', 'friday', 'saterday',
'sunday')
>>> days[:3]
('monday', 'tuesday', ‘wednesday')
>>> days[0:2]
('monday', 'tuesday')

Dictionaries
person = {'Name': 'Tom', 'Age': 27};
print person['Name']; # Tom
print person['Age']; # 27
Python
$person = array('Name' => 'Tom', 'Age' => 27);
print $person['Name'];
print $person['Age'];
PHP

Membership operators
in Evaluates to true if in sequence
not in Evaluates to true if not in sequence
Python has membership operators, which test for membership
in a sequence, such as strings, lists, or tuples

Membership operators (example)
>>> a = (1,2,4,8)
>>> 1 in a
True
>>> 3 not in a
True
>>> 3 in a
False
>>> word = "boat"
>>> 'e' in word
False
>>> 'a' in word
True

Add / multiply operators and
sequences
>>> a = [ 1, 2 ]
>>> b = [ 3, 4 ]
>>> a + b
[1, 2, 3, 4]
>>> a * 4
[1, 2, 1, 2, 1, 2, 1, 2] 
 
>>> a = "hello "
>>> b = "world"
>>> a + b
'hello world'
>>> a * 4
'hello hello hello hello '

Whitespace - indentation
Instead of using curly braces ( { ) to delimit
program blocks, Python uses indentation

It is mandatory, no way around it

It is a very controversial feature that some really
hate…

… but it does improve readability…

… and after a while you totally forget about it.

Conditional: if…else…el(se)if (example)
if (statement) {
// do stuff
} elseif (other_statement) {
// do other stuff
} else {
// do other stuff
}
PHP
if (statement):
# do stuff
elif (other_statement):
# do other stuff
else:
# do other stuff
Python

Iterations: for loop
Python for statement has a lot in common with
PHP foreach

Supports break and continue which works more
or less the same as in PHP

You can loop over strings, lists, dictionaries, … as
they are sequences.

Iterations: for loop (example)
$words = array('cat', 'window', 'door');
foreach ($words as $word) {
echo $word;
}
PHP
words = ['cat', 'window', 'door']
for word in words:
print word
>>> cat, window, door
for word in words[1:3]:
print word
>>> window, door
Python

Iterations: for loop (example)
$persons = array('name' => 'glenn', 'job' => 'developer');
foreach ($persons as $key => $value) {
// process person
}
PHP
persons = {'name': 'glenn', 'job': 'developer'}
for key in persons.keys():
# process key
for value in persons.values():
# process value
for key, value in persons.items(): 
# process value
Python

Iterations: range
If you do need to iterate over a sequence of numbers, you
can use the range() method.

You have also xrange:

if you do range(1, 10000) it will create a list of 10000
elements in memory

when using xrange you create a sequence which
evaluates lazy. This is faster and uses less memory.

In Python 3.x range() -> xrange()

Iterations: range (example)
// array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
$arr = range(1,10);
// array(1, 2, 3, 4, 5, 6,)
foreach (range(1, 6) as $number) {
echo $number;
}
PHP
>>> range(10) # python 2.x
>>> list(range(10)) # python 3.x
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> for number in range(1,6):
print number
>>> 1, 2, 3, 4, 5
Python

Iterations: enumerate (example)
>>> # bad example!
>>> words = ['Mary', 'had', 'a', 'little', 'lamb']
>>> for i in range(len(words)):
print i, words[i]
Bad
>>> # if you need indices use enumerate
>>> words = ['Mary', 'had', 'a', 'little', 'lamb']
>>> for index, value in enumerate(words):
print index, value
Good
For example: when you want index -> value from a list.

Functions
Function blocks begin with the keyword def followed
by the function name and parentheses (( ))

The code block within every function starts with a
colon (:) and is indented.

Functions can have docstring. Accessible through
function.__doc__ or help(function)

Functions (example)
function hello() {
echo "hello world";
}
PHP
def hello():
"Prints hello world" 
echo "hello world"
>>> help(hello)
Help on function hello in module __main__:
hello()
Prints hello world
Python

Function arguments
You can call a function by using the following types
of formal arguments:

Required arguments

Default arguments

Keyword arguments

Variable-length arguments (Variadic function)

PHP >= 5.6 splat operator (…)

Like PHP it doesn’t support function overloading

Required argument (example)
>>> def hello(name):
print "hello" + name
>>> hello("glenn")
glenn
Python
function hello($name) {
echo "hello" . $name;
}
hello("glenn");
PHP

Required argument (example)
>>> def hello(name):
>>> hello()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: hello() takes exactly 1 argument (0 given)

Default argument (example)
>>> def hello(name="glenn"):
>>> hello()
hello glenn
Python
function hello($name="glenn") {
echo “hello” . $name;
}
hello();
>>> hello glenn
PHP

Keyword argument (example)
>>> def sum(a=1, b=2):
print a + b
>>> sum()
3
>>> sum(a=5)
7
>>> sum(b=4)
5
>>> sum(a=2, b=4)
6
Python
( There isn’t a PHP equivalent )

Variable length argument (example)
def manyArgs(*arg):
print "I was called with", len(arg), "arguments:", arg
>>> manyArgs(1)
I was called with 1 arguments: (1,)
>>> manyArgs(1, 2, 3)
I was called with 3 arguments: (1, 2, 3)
Python
function manyArgs(...$arg) {
echo "I was called with " . count($arg) . " arguments: "
implode($arg);
}
hello(1); // I was called with 1 arguments: 1 
hello(1, 2, 3); // I was called with 3 arguments: 1,2,3
PHP >= 5.6 using the . . . (splat) operator

Classes
In Python everything is an object (again)

Class blocks begin with the keyword class followed by
the class name and a colon (:)

Doesn’t have private / public concept

There is a convention that is followed by most Python
code: a name preﬁxed with an underscore (e.g.
_spam) should be treated as a non-public…

…but it is still accessible

Classes can also have docstring.

Classes (example)
class Employee:
def __init__(self, name, salary):
self.name = name
self.salary = salary
e = Employee("mike", "1500")
Python
class Employee {
function __construct($name, $salary) {
$this->name = $name;
$this->salary = $salary;
}
}
$e = new Employee("mike", "1500");
PHP

Classes: inheritance
Supports multiple inheritance (PHP lacks that)

Method overloading works the same as in PHP

You can (optionally) make your base class inherit
from the class object. Matter of style.

Classes: inheritance (example)
class Vehicle {
// vehicle methods and members
}
class Car extends Vehicle {
// car methods and members
}
PHP
class Vehicle:
# vehicle methods and members
class Car(Vehicle):
# car methods and members
Python

Classes: overloading 1/2 (example)
class Parent(object):
def __init__(self):
self.value = 5
def get_value(self):
return self.value
class Child(Parent):
pass # is a null operation
>>> c = Child()
>>> c.get_value()
5

Classes: overloading 2/2 (example)
class Parent(object):
def __init__(self):
self.value = 5
return self.value
class Child(Parent):
return self.value + 1
>>> c = Child()
>>> c.get_value()
6

__init__ /__keyword__
The __keyword__ are also called dunder methods
(thunder in West Flemish or double under)

They are also sometimes called “magic” methods

They are roughly the same as inheriting things

In the case of __init__ in the background Python will do
automatically the calls to init and new

They also make it possible (but are not limited) to change
how operators (for example +, / , ..) behave.

from __future__ import division
(example)
# in python 2.x if you divide an integer you
# will get an integer back
>> 1 / 2
0
# In python 2.7 future = Python 3.x
from __future__ import division
>> 1 / 2
0.5
>> 1 // 2 # you will need the special // division
# operator to get an integer back

File I/O (example)
# Reading a file
with open('myfile.txt', 'r') as f:
for line in f:
print f
# Writing a file
with open('myfile.txt', 'w') as f:
f.write('Hello')

Lambda functions
# Simple lambda example
f = lambda x, y : x + y
>> f(2,4)
6
# Map -> lambda (divide by 2)
>>> a = [2, 4, 8, 16]
>>> map ( lambda x: x/2, a)
[1, 2, 4, 8]
# Filter -> lambda (even numbers)
>>> a = [1, 2, 3, 4, 5, 6 , 7, 8, 9, 10]
>>> filter (lambda x: x % 2 == 0, a)
[2, 4, 6, 8, 10]

The proof is
in the pudding…

Minimal ﬂask (example)
from flask import Flask
app = Flask(__name__)
@app.route("/")
def hello():
return "Hello World!"
@app.route("/name/<name>")
def hello(name=None):
return “Hello “ + name
if __name__ == "__main__":
app.run()
HTTP://FLASK.POCOO.ORG

Minimal scraper 1/2 (example)
<div title="buyer-name">Carson Busses</div>
<span class="item-price">$29.95</span>
HTML
from lxml import html
import requests
page = requests.get('http://econpy.pythonanywhere.com/ex/001.html')
tree = html.fromstring(page.text)
#This will create a list of buyers:
buyers = tree.xpath('//div[@title="buyer-name"]/text()')
#This will create a list of prices
prices = tree.xpath('//span[@class="item-price"]/text()')
print 'Buyers: ', buyers
print 'Prices: ', prices
Python

Minimal scraper 2/2 (example)
Buyers: ['Carson Busses', 'Earl E. Byrd', 'Patty Cakes',
'Derri Anne Connecticut', 'Moe Dess', 'Leda Doggslife', 'Dan Druff',
'Al Fresco', 'Ido Hoe', 'Howie Kisses', 'Len Lease', 'Phil Meup',
'Ira Pent', 'Ben D. Rules', 'Ave Sectomy', 'Gary Shattire',
'Bobbi Soks', 'Sheila Takya', 'Rose Tattoo', 'Moe Tell']
Prices: ['$29.95', '$8.37', '$15.26', '$19.25', '$19.25',
'$13.99', '$31.57', '$8.49', '$14.47', '$15.86', '$11.11',
'$15.98', '$16.27', '$7.50', '$50.85', '$14.26', '$5.68',
'$15.00', '$114.07', '$10.09']
Result
HTTP://DOCS.PYTHON-GUIDE.ORG/EN/LATEST/SCENARIOS/SCRAPE/

Bayesian text classiﬁer
from sklearn.feature_extraction.text import CountVectorizer
from sklearn.pipeline import Pipeline
from sklearn.naive_bayes import MultinomialNB
import numpy
# docs
docs = numpy.array(["Buy viagra", "Hello frank", "The servers are down", "Do
you want a rolex", "Cheap airplane tickets"])
# labels 1: spam, 0: ham
labels = numpy.array([1,0,0,1,1])
# pipeline
steps = [('vectorizer', CountVectorizer()), ('clf', MultinomialNB())]
pipe = Pipeline(steps)
pipe.fit(docs, labels)
# test data
test_data = numpy.array([ "Hello koen", "Cheap viagra"])
print pipe.predict(test_data)
HTTP://SCIKIT-LEARN.ORG/STABLE/

Automate with fabric
# Import Fabric's API module
from fabric.api import *
env.hosts = [‘server.domain.tld’, ‘another_server.domain.tld’]
def update_upgrade():
"""
Update the default OS installation's
basic default tools.
"""
run("aptitude update")
run("aptitude -y upgrade")
def install_memcached():
""" Download and install memcached. """
run("aptitude install -y memcached")
def update_install():
# Update
update_upgrade()
# Install
install_memcached()
HTTP://WWW.FABFILE.ORG/

Some interesting resources
Dive into python -http://www.diveintopython.net/

The standard python library - http://eﬀbot.org/zone/librarybook-
index.htm

How to think like a computer scientist with python - http://
www.greenteapress.com/thinkpython/thinkCSpy.pdf

PyVideo (indexes a lot of python talks) - http://pyvideo.org/

80 best python resources - http://www.fromdev.com/2014/03/
python-tutorials-resources.html

10 myths of enterprise python - https://www.paypal-
engineering.com/2014/12/10/10-myths-of-enterprise-python/

Python success stories - https://www.python.org/about/success/

Thank you for listening…
(any questions ?)

Python: an introduction for PHP webdevelopers

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