print("Hello world!")

# <--- This is a comment. This line is ignored by Python

a = 1
b = 2
print(a+b , a-b , a*b , a/b, a//b)  # Addition, subtraction, multiplication, real division, floor division

# Note: in Python 3,  1/2 = 0.5.  In older versions (Python 2), 1/2 = 0 (Integer division)

b += 1   # increase value of b
print(b)  

a = b**2  # a is now equal to 9 (b*b). Note that I can freely redefine a even if it was already defined

print(a%2 , a%3)  # Remainder of integer vision

a_int = 5      # Integer
a_float = 5.0  # Float
a_str = "5.0"  # String of characters
a_bool = True  # Can also be False

# Type conversion
print(a_str, float(a_str)) # Convert string to float
print(a_int, bool(a_int))# 5 is non-zero and therefore evaluates to True
print(a_int, str(a_int)) # Convert integer to string
print(a_str, int(float(a_str)))  # Convert string to float then integer

for i in range(5):
    print("Loop stage:", i)   # Note the indentation used to define blocks (inside the loop: indented.)

i += 1   # variable i still exists after the loop
print(i)

while i < 10:
    i += 1
print(i)

# In a Jupyter Notebook, variables from previous cells still exist

if i < 10 :
    print("i lower than 10")
elif i > 10:
    print("i greater than 10")
else:
    print("i exactly 10 : ", i==10)    #  a single = means assigning a value. A double == means testing equality

# greater or equal: >=   ;   lower or equal: <=

def someTestFunction(x,y):
    return x*y

print(someTestFunction(4,5))
print(someTestFunction(94,107))

a = [1,2,3,4,5]
b = [8.0,'foo',True,2,"bar"]  # A list can hold several types. Strings can be delimited by either ' or " 

print("Iterating on list a:")
for x in a:
    print(x)
    
print("Iterating on both lists:")
if len(a) == len(b):
    for i in range(len(a)):
        print(a[i],b[i])
        
b.append(42)  # Lists are dynamic, can always add stuff
b.append(a)   # Lists can contain other lists

print("Enumerating modified list b:")
for i,x in enumerate(b):
    print(i,x)

c = b.pop()   # Remove last element of the list
print(c == a) # ... which happens to be list a
print(b)      # Can print a list directly - see that its last element is gone now

print("---")
# We can access individual elements of the list:
print(b[0],b[1])  # First two
print(b[-1],b[-2])# Last two
# and we can slice the list:
print(b[2:]) # All elements from number 2 to the last

# Strings are lists too!

hw = "Hello World!"

for x in hw: print(x)
    
print(hw.split(' ')[1]) # Separate into two substring using whitespace as delimiter, then print the second part

print(hw.replace('World','All')) # String substitution

print(hw + 'How are you?')   # String concatenation

a = {'foo':58,'bar':42,8:5}   # Unordered list where each object is assigned a name, a "key"
                              # Keys can be string, integer, ...
print(a['foo'])
print(a[8])         # Access the element named "8"

for x in a.keys(): print(x)   # Iterate on the list of keys

if 'foo' in a.keys() and 'bar' in a.keys():
    print("Good keys. Sum:",a['foo'] + a['bar'])

# Classic syntax

myfile = open('demo.txt','w')   # 'w' : open in 'write' mode
myfile.write('foo')
myfile.close()

# New/recommended python syntax
with open('demo.txt','w') as myfile:    # I open the same file: it is erased
    myfile.write('foo')         #  Indented block. The file is closed automatically at the end of the block
    
# Write a list to a file, line by line
a = ['a','b','c','d']
with open('demo.txt','w') as myfile:
    for item in a :
        myfile.write(item + '\n')   # '\n' : linebreak
    
# Read that file, line by line
with open('demo.txt','r') as myfile:   # 'r' : open in 'read' mode
    b = []
    for line in myfile:
        b.append( line.rstrip('\n'))    # Remove the '\n' linebreak character
        
print(b == a)    # Should be True

import time  # Use the library relative to time

currentTime = time.time()  # Get current epoch in seconds
time.sleep(5)              # Sleep for 5 seconds
elapsedTime = time.time() - currentTime

print("Slept for {} seconds".format(elapsedTime))  # Note the way I insert a variable into a string

from math import pi   # I only want pi from that library and nothing else, so I don't need to write "math.pi"

print(pi)

from math import log as ln  # I can rename a library or function when importing it

print(ln(2.7))

%matplotlib inline 
# The above line is for Jupyter Notebooks only 
import matplotlib.pyplot as plt    # Import plotting library - I write this line so much I have muscle memory for it

plt.plot([1,2,3],[1,4,9])

fig1 = plt.figure() 

x = range(-10,20,2)
y_quadratic = [a**2 for a in x]   # Create a list in a single line
y_cubic = [a**3 for a in x]

plt.plot(x,y_quadratic,'--',label='quad',color='blue')
plt.plot(x,y_cubic,'o-',label='cube',color='red')
plt.xlabel('Horizontal Axis')
plt.ylabel('Vertical Axis')
plt.title("Full demo")
plt.legend(loc='best')  # Can also specify 'upper left', 'lower right', etc
plt.xlim((-15,25))  # Limits on the x-axis
#plt.yscale('log')  # In case you want a logarithmic plot
plt.text(0,3000,'Some text',fontsize='12',rotation=30,color='green')

a = [1,2,3,4]
b = a        # Is this a copy? Or a pointer?

b.append(5)  # If it was a copy, then a and b should be different now

print(a,b)   # Modifying b also modifies a.
print(a is b) # They are still the same. 
print('---')

# Here is a workaround
c = [x for x in a]  # I specify that the list should have the same content, instead of being the same
c.append(6)

print(a,c)   # Here I changed c but I didn't change a. 
             # Be careful however: if 'a' contains a list, then you can run in the same problem


# You can use the Python library 'copy' (with a 'deep copy') to make 100% sure you won't have that issue

import this