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====== Notes Python ======

Sources :

  * https://www.tutorialspoint.com/python3/index.htm

Aller plus loin :

  * https://medium.com/activewizards-machine-learning-company/top-15-python-libraries-for-data-science-in-in-2017-ab61b4f9b4a7

===== Bases =====

<code python>
#!/usr/bin/python3

# output
print ("Hello, Python!")
print(x, end=" ")  # Appends a space instead of a newline in Python 3

# input
x = input("something:")

# raise exception
raise IOError("file error") #this is the recommended syntax in Python 3
</code>

<code python>
# Quotation in Python
word = 'word'
sentence = "This is a sentence."
paragraph = """This is a paragraph. It is
made up of multiple lines and sentences."""
</code>


===== Variable Types =====

<code python>
# Simple Assignment
counter = 100          # An integer assignment
miles   = 1000.0       # A floating point
value   = 3e+26J       # A complex
name    = "John"       # A string

# Multiple Assignment
a = b = c = 1
a, b, c = 1, 2, "john"

# deletion
a, b, c = 1, 2, "john"
</code>

<code python>
str = 'Hello World!'

print (str)          # Prints complete string
print (str[0])       # Prints first character of the string
print (str[2:5])     # Prints characters starting from 3rd to 5th
print (str[2:])      # Prints string starting from 3rd character
print (str * 2)      # Prints string two times
print (str + "TEST") # Prints concatenated string
</code>

<code python>
list = [ 'abcd', 786 , 2.23, 'john', 70.2 ]
tinylist = [123, 'john']

print (list)          # Prints complete list
print (list[0])       # Prints first element of the list
print (list[1:3])     # Prints elements starting from 2nd till 3rd 
print (list[2:])      # Prints elements starting from 3rd element
print (tinylist * 2)  # Prints list two times
print (list + tinylist) # Prints concatenated lists
</code>

<code python>
tuple = ( 'abcd', 786 , 2.23, 'john', 70.2  )
tinytuple = (123, 'john')

print (tuple)           # Prints complete tuple
print (tuple[0])        # Prints first element of the tuple
print (tuple[1:3])      # Prints elements starting from 2nd till 3rd 
print (tuple[2:])       # Prints elements starting from 3rd element
print (tinytuple * 2)   # Prints tuple two times
print (tuple + tinytuple) # Prints concatenated tuple
</code>

<code python>
dict = {}
dict['one'] = "This is one"
dict[2]     = "This is two"

tinydict = {'name': 'john','code':6734, 'dept': 'sales'}

print (dict['one'])       # Prints value for 'one' key
print (dict[2])           # Prints value for 2 key
print (tinydict)          # Prints complete dictionary
print (tinydict.keys())   # Prints all the keys
print (tinydict.values()) # Prints all the values
</code>

<code python>
#Data Type Conversion
int(x [,base]) #Converts x to an integer. The base specifies the base if x is a string.
float(x) # Converts x to a floating-point number.
complex(real [,imag]) # Creates a complex number.
str(x) # Converts object x to a string representation.
repr(x) # Converts object x to an expression string.
eval(str) # Evaluates a string and returns an object.
tuple(s) # Converts s to a tuple.
list(s) # Converts s to a list.
set(s) # Converts s to a set.
dict(d) # Creates a dictionary. d must be a sequence of (key,value) tuples.
frozenset(s) # Converts s to a frozen set.
chr(x) # Converts an integer to a character.
unichr(x) # Converts an integer to a Unicode character.
ord(x) # Converts a single character to its integer value.
hex(x) # Converts an integer to a hexadecimal string.
oct(x) # Converts an integer to an octal string.
</code>

===== Basic Operators =====

<code python>
# Python Arithmetic Operators
c = a % b  # Modulus
c = a ** b # Exponent
c = a // b # Floor Division

# Python Membership Operators
x in y
x not in y

# Python Identity Operators
x is y
x is not y
</code>

===== Decision Making =====

<code python>
# if statement
if expression:
   statement(s)
   
# if else statement
if expression:
   statement(s)
else:
   statement(s)
   
# nested if statements
if expression1:
   statement(s)
elif expression:
   statement(s)
else:
   statement(s)

# Single Statement if
if ( var  == 100 ) : print ("Value of expression is 100")
</code>


===== Decision Making =====

<code python>
# while loop
while expression:
   statement(s)
   
while count < 5:
   count = count + 1
else:
   print (count, " is not less than 5")
   
   
# for loop
for iterating_var in sequence:
   statements(s)
   
>>> range(5)
range(0, 5)
>>> list(range(5))
[0, 1, 2, 3, 4]

fruits = ['banana', 'apple',  'mango']
for index in range(len(fruits)):
   print ('Current fruit :', fruits[index])
   
for num in numbers:
   if num%2 == 0:
      print ('the list contains an even number')
      break
else:
   print ('the list doesnot contain even number')

# Loop Control Statements
break
continue
pass
</code>

<code python>
# Iterators
list = [1,2,3,4]
it = iter(list) # this builds an iterator object
print (next(it)) #prints next available element in iterator

# Iterator object can be traversed using regular for statement
for x in it:
   print (x, end=" ")
   
# or using next() function
while True:
   try:
      print (next(it))
   except StopIteration:
      sys.exit() #you have to import sys module for this
</code>

<code python>
# Generators

import sys
def fibonacci(n): #generator function
   a, b, counter = 0, 1, 0
   while True:
      if (counter > n): 
         return
      yield a
      a, b = b, a + b
      counter += 1
f = fibonacci(5) #f is iterator object

while True:
   try:
      print (next(f), end=" ")
   except StopIteration:
      sys.exit()
</code>


===== Numbers =====

<code python>
number = 1 # int
number = 1.2 # float
number = -32.54e100
number = 1 + 2J #complex
number = 0xA0F #Hexa-decimal = 2575
number = 0o37 #Octal = 31

# Number Type Conversion
int(x) 
long(x)
float(x) 
complex(x) 
complex(x, y)

# Mathematical Functions
abs(x)
ceil(x)
cmp(x, y) # Deprecated
exp(x)
fabs(x)
floor(x)
log(x)
log10(x)
max(x1, x2,...)
min(x1, x2,...)
modf(x)
pow(x, y)
round(x [,n])
sqrt(x)

# Random Number Functions
choice(seq)
randrange ([start,] stop [,step])
random()
seed([x])
shuffle(lst)
uniform(x, y)

# Trigonometric Functions
acos(x)
asin(x)
atan(x)
atan2(y, x)
cos(x)
hypot(x, y)
sin(x)
tan(x)
degrees(x)
radians(x)

# Mathematical Constants
pi
e
</code>


===== Strings =====

<code python>
var1 = 'Hello World!'
var2 = "Python Programming"

# substrings
var1[0]
var2[1:5]

# String Special Operators
a + b
a * n
a[n] # slice
a[n:m] # range slice
a in b
a in not b
r'...' # raw string
R'...' # raw string
</code>

<code python>
# String Formatting Operator
print ("My name is %s and weight is %d kg!" % ('Zara', 21)) 

%c character	
%s string conversion via str() prior to formatting	
%i signed decimal integer	
%d signed decimal integer	
%u unsigned decimal integer	
%o octal integer
%x hexadecimal integer (lowercase letters)	
%X hexadecimal integer (UPPERcase letters)	
%e exponential notation (with lowercase 'e')	
%E exponential notation (with UPPERcase 'E')	
%f floating point real number
%g the shorter of %f and %e	
%G the shorter of %f and %E

*     argument specifies width or precision
-     left justification	
+     display the sign	
<sp>  leave a blank space before a positive number	
#     add the octal leading zero ( '0' ) or hexadecimal leading '0x' or '0X', 
      depending on whether 'x' or 'X' were used.
0     pad from left with zeros (instead of spaces)
%     '%%' leaves you with a single literal '%'
(var) mapping variable (dictionary arguments)
m.n.  m is the minimum total width and n is the number of digits to display 
      after the decimal point (if appl.)

# Triple Quotes
para_str = """this is a long string that is made up of
several lines and non-printable characters such as
TAB ( \t ) and they will show up that way when displayed.
the variable assignment will also show up.
"""
</code>

<code python>
# Unicode String
capitalize()
center(width, fillchar)
count(str, beg = 0,end = len(string))
decode(encoding = 'UTF-8', errors = 'strict')
encode(encoding = 'UTF-8', errors = 'strict')
endswith(suffix, beg = 0, end = len(string))
expandtabs(tabsize = 8)
find(str, beg = 0 end = len(string))
index(str, beg = 0, end = len(string))
isalnum()
isalpha()
isdigit()
islower()
isnumeric()
isspace()
istitle()
isupper()
join(seq)
len(string)
ljust(width[, fillchar])
lower()
lstrip()
maketrans()
max(str)
min(str)
replace(old, new [, max])
rfind(str, beg = 0,end = len(string))
rindex( str, beg = 0, end = len(string))
rjust(width,[, fillchar])
rstrip()
split(str="", num=string.count(str))
splitlines( num=string.count('\n'))
startswith(str, beg=0,end=len(string))
strip([chars])
swapcase()
title()
translate(table, deletechars="")
upper()
zfill (width)
isdecimal()
</code>


===== List =====

<code python>
list1 = ['physics', 'chemistry', 1997, 2000]
list2 = [1, 2, 3, 4, 5 ]
list3 = ["a", "b", "c", "d"]

# get
list1[0]
list2[1:5]
L[2]	
L[-2]	
L[1:]

# set
list[2] = 2001

# remove
del list[2]

# Basic List Operations
len([1, 2, 3])          # length
[1, 2, 3] + [4, 5, 6]   # concatenation
['Hi!'] * 4             # repetition
3 in [1, 2, 3]          # membership

for x in [1,2,3] : print (x,end = ' ')

# Built-in List Functions and Methods
cmp(list1, list2) # obsolete
len(list)
max(list)
min(list)
list(seq)

list.append(obj)
list.count(obj)
list.extend(seq)
list.index(obj)
list.insert(index, obj)
list.pop(obj = list[-1])
list.remove(obj)
list.reverse()
list.sort([func])
</code>


===== Tuples =====

<code python>
tup1 = ('physics', 'chemistry', 1997, 2000)
tup2 = (1, 2, 3, 4, 5 )
tup3 = "a", "b", "c", "d"

tup1 = (); # empty tuple
tup1 = (50,)

# Accessing Values in Tuples
tup1[0]
tup2[1:5]

# Updating Tuples
tup3 = tup1 + tup2 # concatenate
del tup

# Basic Tuples Operations
len((1, 2, 3))	        # Length
(1, 2, 3) + (4, 5, 6)   # concatenation
('Hi!',) * 4            # repetition
3 in (1, 2, 3)          # membership

for x in (1,2,3) : print (x, end = ' ')	

# Indexing, Slicing, and Matrixes
T[2]	
T[-2]	
T[1:]

# Built-in Tuple Functions
cmp(tuple1, tuple2)
len(tuple)
max(tuple)
min(tuple)
tuple(seq)
</code>


===== Dictionary =====

<code python>
dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'}
dict['Age']

# Updating Dictionary
dict['Age'] = 8; # update existing entry
dict['School'] = "DPS School" # Add new entry

# Delete Dictionary Elements
del dict['Name'] # remove entry with key 'Name'
dict.clear()     # remove all entries in dict
del dict         # delete entire dictionary

# Built-in Dictionary Functions and Methods
cmp(dict1, dict2)
len(dict)
str(dict)
type(variable)

dict.clear()
dict.copy()
dict.fromkeys()
dict.get(key, default=None)
dict.has_key(key)
dict.items()
dict.keys()
dict.setdefault(key, default = None)
dict.update(dict2)
dict.values()
</code>


===== Date and time =====

<code python>
import time;  # This is required to include time module.

ticks = time.time()
print ("Number of ticks since 12:00am, January 1, 1970:", ticks)

> time.struct_time(tm_year = 2016, tm_mon = 2, tm_mday = 15, tm_hour = 9, 
   tm_min = 29, tm_sec = 2, tm_wday = 0, tm_yday = 46, tm_isdst = 0)
   
# Getting current time
localtime = time.localtime(time.time())
localtime = time.asctime( time.localtime(time.time()) ) # formatted

# The time Module
time.altzone
time.asctime([tupletime])
time.clock( )
time.ctime([secs])
time.gmtime([secs])
time.localtime([secs])
time.mktime(tupletime)
time.sleep(secs)
time.strftime(fmt[,tupletime])
time.strptime(str,fmt = '%a %b %d %H:%M:%S %Y')
time.time( )

time.timezone
time.tzname
</code>

<code python>
import calendar

cal = calendar.month(2016, 2)
print ("Here is the calendar:")
print (cal)

# affiche:
Here is the calendar:
   February 2016
Mo Tu We Th Fr Sa Su
 1  2  3  4  5  6  7
 8  9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29

# The calendar Module
calendar.calendar(year,w = 2,l = 1,c = 6)
calendar.firstweekday( )
calendar.isleap(year)
calendar.leapdays(y1,y2)
calendar.month(year,month,w = 2,l = 1)
calendar.monthcalendar(year,month)
calendar.monthrange(year,month)
calendar.prcal(year,w = 2,l = 1,c = 6)
calendar.prmonth(year,month,w = 2,l = 1)
calendar.setfirstweekday(weekday)
calendar.timegm(tupletime)
calendar.weekday(year,month,day)
</code>


===== Functions =====

<code python>
# Syntax
def functionname( parameters ):
   "function_docstring"
   function_suite
   return [expression]
   
# Function definition is here
def printme( str ):
   "This prints a passed string into this function"
   print (str)
   return

# Now you can call printme function
printme("This is first call to the user defined function!")
printme("Again second call to the same function")   

# All parameters (arguments) in the Python language are passed by reference. 

# Required Arguments
def printme( str ): 

# Keyword Arguments
printme( str = "My string")

# Default Arguments
def printinfo( name, age = 35 ):

#Variable-length Arguments
def functionname([formal_args,] *var_args_tuple ):
   "function_docstring"
   function_suite
   return [expression]

# Function definition is here
def printinfo( arg1, *vartuple ):
   "This prints a variable passed arguments"
   print ("Output is: ")
   print (arg1)
   for var in vartuple:
      print (var)
   return

# Now you can call printinfo function
printinfo( 10 )
printinfo( 70, 60, 50 )

#The return Statement
def sum( arg1, arg2 ):
   return total
   
total = sum( 10, 20 )
</code>

<code python>
# The Anonymous Functions
lambda [arg1 [,arg2,.....argn]]:expression

# Function definition is here
sum = lambda arg1, arg2: arg1 + arg2


# Now you can call sum as a function
print ("Value of total : ", sum( 10, 20 ))
print ("Value of total : ", sum( 20, 20 ))
</code>


===== Modules =====

<code python>
# The import Statement
import module1[, module2[,... moduleN]

# support.py
def print_func( par ):
   print "Hello : ", par
   return
   
#usage
import support

support.print_func("Zara")
</code>

<code python>
# The from...import Statement
from modname import name1[, name2[, ... nameN]]

# fib.py
def fib(n): # return Fibonacci series up to n
   result = []
   a, b = 0, 1
   while b < n:
      result.append(b)
      a, b = b, a + b
   return result

#usage
from fib import fib
</code>

<code python>
# The from...import * Statement
from modname import *
</code>

<code python>
# Executing Modules as Scripts
#!/usr/bin/python3

# Fibonacci numbers module

def fib(n): # return Fibonacci series up to n
   result = []
   a, b = 0, 1
   while b < n:
      result.append(b)
      a, b = b, a + b
   return result
if __name__ == "__main__":
   f = fib(100)
   print(f)
</code>

the following sequences

  - The current directory.
  - If the module is not found, Python then searches each directory in the shell variable PYTHONPATH.
  - If all else fails, Python checks the default path. On UNIX, this default path is normally /usr/local/lib/python3/.

The sys.path variable contains the current directory, PYTHONPATH, and the installation-dependent default.

<code python>
dir(plugin)
locals()
globals()
reload(plugin)
</code>

<code python>
# Packages in Python
Phone/Pots.py
Phone/IsDn.py
Phone/G3.py

# Phone/__init__.py
from Pots import Pots
from Isdn import Isdn
from G3 import G3

# uses
import Phone

Phone.Pots()
Phone.Isdn()
Phone.G3()
</code>


===== Files I/O =====

<code python>
#Printing to the Screen
print ("Python is really a great language,", "isn't it?")

#The input Function
x = input("something:")
</code>

<code python>
# The open Function
file object = open(file_name [, access_mode][, buffering])
access_mode = r/r+/w/w+/a, b

# Open a file
fileObject.close();

fo = open("foo.txt", "wb")
print ("Name of the file: ", fo.name)
print ("Closed or not : ", fo.closed)
print ("Opening mode : ", fo.mode)
fo.close()

# The write() Method
fileObject.write(string);

fo = open("foo.txt", "w")
fo.write( "Python is a great language.\nYeah its great!!\n")
fo.close()

# The read() Method
fileObject.read([count]);

fo = open("foo.txt", "r+")
str = fo.read(10)
print ("Read String is : ", str)
fo.close()

# File Positions
position = fo.tell()
position = fo.seek(0, 0)

# Renaming and Deleting Files
os.rename(current_file_name, new_file_name)
os.remove(file_name)
os.mkdir(dir_name)
os.chdir(dire_name)
os.getcwd()
os.rmdir(dir_name)
</code>


===== Exceptions Handling =====

<code python>
# Standard Exceptions
Exception # Base class for all exceptions
StopIteration # Raised when the next() method of an iterator does not point to any object.
SystemExit # Raised by the sys.exit() function.
StandardError # Base class for all built-in exceptions except StopIteration and SystemExit.
ArithmeticError # Base class for all errors that occur for numeric calculation.
OverflowError # Raised when a calculation exceeds maximum limit for a numeric type.
FloatingPointError # Raised when a floating point calculation fails.
ZeroDivisonError # Raised when division or modulo by zero takes place for all numeric types.
AssertionError # Raised in case of failure of the Assert statement.
AttributeError # Raised in case of failure of attribute reference or assignment.
EOFError # Raised when there is no input from either the raw_input() or input() function and
         # the end of file is reached.
ImportError # Raised when an import statement fails.
KeyboardInterrupt # Raised when the user interrupts program execution, usually by pressing Ctrl+c.
LookupError # Base class for all lookup errors.
IndexError # Raised when an index is not found in a sequence.
KeyError # Raised when the specified key is not found in the dictionary.
NameError # Raised when an identifier is not found in the local or global namespace.
UnboundLocalError # Raised when trying to access a local variable in a function or method  
                  # but no value has been assigned to it.
EnvironmentError # Base class for all exceptions that occur outside the Python environment.
IOError # Raised when an input/ output operation fails, such as the print statement or the 
        # open() function when trying to open a file that does not exist.
OSError # Raised for operating system-related errors.
SyntaxError # Raised when there is an error in Python syntax.
IndentationError # Raised when indentation is not specified properly.
SystemError # Raised when the interpreter finds an internal problem, but when this error 
            # is encountered the Python interpreter does not exit.
SystemExit # Raised when Python interpreter is quit by using the sys.exit() function.
           # If not handled in the code, causes the interpreter to exit.
TypeError # Raised when an operation or function is attempted that is invalid for the specified data type.
ValueError # Raised when the built-in function for a data type has the valid type of arguments,
           # but the arguments have invalid values specified.
RuntimeError # Raised when a generated error does not fall into any category.
NotImplementedError # Raised when an abstract method that needs to be implemented in an
                    # inherited class is not actually implemented.
</code>

<code python>
# assert Statement
assert Expression[, Arguments]

assert (Temperature >= 0), "Colder than absolute zero!"

# Handling an exception
try:
   fh = open("testfile", "w")
   fh.write("This is my test file for exception handling!!")
except IOError:
   print ("Error: can\'t find file or read data")
except AssertionError, SystemExit:
   print ("Error: multiple exceptions")
except ValueError as Argument:
   print ("The argument does not contain numbers\n", Argument)
except:
   print ("Error: all exceptions")
else:
   print ("Written content in the file successfully")
finally:
   fh.close()
   
# Raising an Exception
raise Exception(level)

# User-Defined Exceptions
class Networkerror(RuntimeError):
   def __init__(self, arg):
      self.args = arg
      
try:
   raise Networkerror("Bad hostname")
except Networkerror,e:
   print e.args
</code>



===== Objects =====

<code python>
</code>




<code python>
#!/usr/bin/python

class Employee:
   'Common base class for all employees'
   empCount = 0

   def __init__(self, name, salary):
      self.name = name
      self.salary = salary
      Employee.empCount += 1
   
   def displayCount(self):
     print "Total Employee %d" % Employee.empCount

   def displayEmployee(self):
      print "Name : ", self.name,  ", Salary: ", self.salary

"This would create first object of Employee class"
emp1 = Employee("Zara", 2000)
"This would create second object of Employee class"
emp2 = Employee("Manni", 5000)
emp1.displayEmployee()
emp2.displayEmployee()
print "Total Employee %d" % Employee.empCount
</code>

<code python>
# Built-In Class Attributes
print "Employee.__doc__:", Employee.__doc__
print "Employee.__name__:", Employee.__name__
print "Employee.__module__:", Employee.__module__
print "Employee.__bases__:", Employee.__bases__
print "Employee.__dict__:", Employee.__dict__
</code>

<code python>
# Class Inheritance
class Parent:        # define parent class
   parentAttr = 100
   def __init__(self):
      print "Calling parent constructor"

   def parentMethod(self):
      print 'Calling parent method'

   def setAttr(self, attr):
      Parent.parentAttr = attr

   def getAttr(self):
      print "Parent attribute :", Parent.parentAttr

class Child(Parent): # define child class
   def __init__(self):
      print "Calling child constructor"

   def childMethod(self):
      print 'Calling child method'

c = Child()          # instance of child
c.childMethod()      # child calls its method
c.parentMethod()     # calls parent's method
c.setAttr(200)       # again call parent's method
c.getAttr()          # again call parent's method
</code>

<code python>
# Overriding Methods
class Parent:        # define parent class
   def myMethod(self):
      print 'Calling parent method'

class Child(Parent): # define child class
   def myMethod(self):
      print 'Calling child method'

c = Child()          # instance of child
c.myMethod()         # child calls overridden method
</code>
C++, Qt, OpenGL, CUDA

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