Introduction to python

Introduction to Python
Marian HackMan Marinov <mm@1h.com>
Chief System Architect of SiteGround.com
Marian HackMan Marinov <mm@1h.com> Introduction to Python

Indentation rules
Use only single type of indentation: tabs or spaces
Indentation rules are applied per function, not per file :(
Python allows you to mix spaces and tabs in different functions
Never use different amount of spaces
Never mix tabs and spaces
PEP8 defines 4 spaces as the delimiter for Python
# this is a comment

Documentation
"""
Module documentation
"""
import module_name
print(module_name.__doc__)
print(module_name.func.__doc__)
help(func)

Data types
Numbers - 1234, 3.1415
Strings - ’spam’, "ham’s", b’ax01c’
Lists - [1, [2, ‘three’], 4]
Dicts - {‘food’: ‘jam’, ‘taste’: ‘yummy’}
Tuples - (1, ‘spam’, 4, ‘U’)
Sets - unordered list of unique items
Files - ﬁle = open(‘doors’, ‘r’)
Core - Booleans, types, None

Variable assignments
a = b = 'info'
a, b, c = 42
[ a, b ] = [ "info", "data" ]

Number deﬁnitions
a = 1234 a = -23 a = 0
a = 99999999L a = 42l a = 1.54
a = 3.14e-10 a = 4E210
a = .1 a = 1.

Number operations
X << N, X >> N - bitwise left/right shift
~X - bitwise invert
X ** Y == pow(x,y)
int(X)
long(X)
ﬂoat(X)
pow(x, y, [,z]) Return x to the power y; if z is present, return x
to the power y, modulo z

Number short operators
+= -=
*= %=
etc.

String deﬁnitions
str = "I'm string"
str = 'my string'
str = """block
of long
text
"""
str = "Single" "string" "line"
str = u"unicode string"
str = b'ax01c'

String formating
print("my %s string" % name)
print("my {0} string".format(name))
str = '{0}, {1} and {2}'
str.format('beer', 'rakia', 'wiski')
jolt = """
Greetings %(name)s.
This is your %(count)d visit here.
"""
values = { 'name': 'Pesho', 'count': 13 }
print (jolt % values)
cmp(jolt, jil) # returns -1, 0, 1

String operations
>>> S = "abcd1234"
>>> for x in S: print(x) # char by char
>>> S[0], S[-2]
('a', 3)
>>> S[1:3], S[3:], S[:-2]
('bc', 'd1234', 'abcd12')
>>> len(S)
8
>>> G = "kompot"
>>> S + G # concatenation
'abcd1234kompot'
>>> "5" in S
False
>>> "3" in S
True

String operations
>>> B = list(S) # convert a string into list
>>> line = 'new thing here'
>>> cols = line.split()
['new', 'thing', 'here']
>>> new_line = "AA".join(cols)
'newAAthingAAhere'
>>> new_line.replace('AA', '__')
'new__thing__here'

List operations
>>> L = [ 12, 34, 51 ]
>>> len(L)
3
>>> L[2]
51
>>> L = [ 12, [ 32, 65, 41 ], 51 ]
>>> len(L)
3
>>> L[1][2]
41
>>> L[1:]
[[32, 65, 41], 51]

List operations
>>> L.append('55') # adds 55 to the end of the list
delete and return the last val of the list
>>> L.pop()
>>> L.extend([82, 92]) # add multiple items to the end
>>> A = [ 'for', 'not', 'bare' ]
>>> A.remove('not') # removes an entry from the list
>>> A.index('bare') # returns 2
>>> A.insert(1, 'com') # adds 1 to com
leave only the first val of the list
>>> del A[1:]

Dictionary operations
D = {}
D = { "info": "nodata", "code": 23 }
D = { "info": "nodata", "code": { "num": 23, "text": "missi
D = dict(name="Bob", "age"=40)
D = dict.fromkeys(['a', 'b'])
D["info"]
D["code"]["num"]
"code" in D
D.keys()
D.values()
D.items
D.pop(key) eq del(D[key])
len(D)
D[key] = 42

Tuple operations
() - empty tuple
>>> T = (0,)
>>> T = ( 12, "311", 5 )
>>> T = 12, "311", 5
>>> T = tuple('text')
('t', 'e', 'x', 't')

Set operations
>>> basket = {'app', 'org', 'app', 'par', 'org', 'ban'}
>>> basket # show that duplicates have been removed
{'org', 'ban', 'par', 'app'}
>>> 'orange' in basket # fast membership testing
True
>>> 'crabgrass' in basket
False

Set operations
Demonstrate set operations on unique letters from two words
>>> a = set('abracadabra')
>>> b = set('alacazam')
>>> a # unique letters in a
{'a', 'r', 'b', 'c', 'd'}
>>> a - b # letters in a but not in b
{'r', 'd', 'b'}
>>> a | b # letters in a or b or both
{'a', 'c', 'r', 'd', 'b', 'm', 'z', 'l'}
>>> a & b # letters in both a and b
{'a', 'c'}
>>> a ^ b # letters in a or b but not both
{'r', 'd', 'b', 'm', 'z', 'l'}

File operations
output = open('file1', 'w')
input = open('file1', 'r')
input = open('file1', 'rb') # read binary
input = open('file1') # same as above
str = input.read() # reads entire file
str = input.read(N) # read next N chars
str = input.readline() # read a single line
lines = input.readlines() #read entire file into list
output.write(str)
output.writelines(lines)
fh.seek(N) # seek to offset N
fh.close() # close a file handler
for line in open('data'): print line
open('f.txt', encoding='utf-8')

Program units
Functions
Modules
Classes

Control structures
if-elif-else
while-else
for-else

Control structures - if-elif-else
if <test>:
code
elif <test>:
code
elif <test>:
code
else:
code

Control structures - if-elif-else
if 1: code
A = Y if X else Z
A = [Z, Y][bool(X)]
>>> branch = {'spam': 5, 'ham': 3, 'other': 1.15}
>>> print(branch.get('spam', 'bad value')
5
>>> print(branch.get('spam', 'bad value')
'bad value'

Control structures - while-else
while <test>:
code
else:
code

Control structures - for-else
for <statements>:
code
else:
code

Control structures - nestead list
list_of_lists = [ [1, 2, 3], [4, 5, 6], [7, 8, 9]]
for list in list_of_lists:
for x in list:
print x

Controlling loops
break
continue
pass
the else block

Controlling loops - break
while <test>:
code
if <test>:
break
else:
code

Controlling loops - continue
while <test>:
code
if <test>:
continue
else:
code

Controlling loops - pass
while 1: pass
def func1(name):
pass

Controlling loops - else
while <test>:
code
if <test>:
continue
else:
code

Breaking nestead loops
for x in range(10):
for y in range(10):
print(x*y)
if x*y > 50:
break
else:
continue # executed if the loop ended normally (
break # executed if 'continue' was skipped (break)

for x in range(10):
for y in range(10):
for z in range(10):
print(x,y,z)
if x*y*z == 30:
break
else:
continue
break
else:
continue
break

def your_outer_func():
...
def inner_func():
for x in range(10):
for y in range(10):
print(x*y)
if x*y > 50:
return
inner_func()
...

Functions
def name(VARIABLES)
yield vs return

Calling functions
func(value)
# Keyword argument - matched by name
func(name=value)
# Pass all objects in sequence as individual arguments
func(*sequence)
# Pass all key/value pairs in dict as individual keyword ar
func(**dict)
x = print
x('Indirect call of print')

Function deﬁnitions
def func(name)
def func(name=value)
def func(*name) # args tuple/list
def func(**name) # dict
def func(*args, name)
def func(*, name=value)

Diﬀerence between return and yield
return - returns one value and clear the state of the variables
yield - return a value and save the position
def gensquares(N):
for i in range(N):
yield i ** 2
for i in gensqares(5):
print(i, end=' : ')

Working with modules
Import
From
Reload

Object Oriented Python

zip & map
map(func, *iterables)
zip

Introduction to python

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