Introduction to programming in Python and JavaScript - Issue#3

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• Introduction to programming in Python and JavaScript - Issue#1
• Introduction to programming in Python and JavaScript - Issue#2

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3.4 Lists (also called tables)

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A variable can be assigned a list of elements. This is an enumerationof elements separated by a comma and framed by brackets.
list = ["Alain", "Olivier", "Patrick", "Paul"]

You can display the first item in the list using the command -

JavaScript	Python
document.write(liste[0])	print(liste[0])

Python allows you to create lists of numbers with the range command. Here are three examples of such lists.

list1 = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]
list2 = [20, 30, 40, 50, 60, 70, 80, 90]
list3 = [99, 97, 95, 93, 91, 89, 87, 85, 83, 81, 79, 77, 75, 73, 71]

In JavaScript, you have to program the range function yourself. In addition, before edit a list, called list, item by element (rather than with brackets) it type the list line = Array (n) where n is the number of items in the list.

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3.5 Comparison Operators and Boolean Variables

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A comparison operator associates a proposition with a truth value: (true for true and false for false). This truth value can be assigned to a variable, called Boolean. The negation operator overturns the truth values ​​(true becomes false and vice versa).

Name	JavaScript	Python
is equal to	a == b	a == b
is not equal to	a != b	a != b
is taller than	a > b	a > b
is smaller than	a < b	a < b
is bigger or equal to	a >= b	a >= b
is smaller or equal to	a <= b	a <= b
Logical AND	a && b	a and b
OR logical	a / b	a or b
negation (NOT)	!a	not a

The "exclusive or"

In JavaScript the XOR (or exclusive) seems missing, but we can use that book 1 (instead of true, but which is considered as such) or 0 (instead of false, but which is considered as such).
In Python, the XOR (or exclusive) is given by the operator ^.

Special cases

For JavaScript, the test 2 == "2" gives true. By cons 2 === "2" gives false.
For Python, the test 1 == 1.0 gives true. By cons 1 is 1.0 gives false.

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4 Control structures

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In programming, one needs to perform different actions depending on the current state of the execution of the program. The control structures are there to solve these difficulties.

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4.1 The command "if. . ., so . . . "

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4.1.1 Version simple

if (condition) then (block of instructions).

Code JavaScript -

if (condition) // mandatory parentheses
{
// code that will be executed if the condition is true
// no need to indent (shift right), but
// braces are needed if there is
// several lines of code
}

Code Python -

if condition: ## mandatory double-points
## code that will be executed if the condition is true
## this code must be indented (shifted right)
## as soon as the indentation stops, we leave the "if"

Example:-

x = 5
if (x == 5)
{
document.write ("x is 5.")
document.write ("If, if!")
}
document.write ("Out of the yew")

x = 5
if x == 5:
print ("x is 5.")
print ("Si, si!")
print ("Out of the yew")

4.1.2 Usual version

if (condition) then (1st block of instructions), otherwise (2nd block of instructions).

Code JavaScript

if (condition) // mandatory parentheses
{
// code that will be executed if the condition is true
}
else
{
// code that will be executed if the condition is false
}

Code Python

if condition: ## mandatory double-points
## code that will be executed if the condition is true
else:
## code that will be executed if the condition is false

Example:-

x = 5
if (x == 5)
{
document.write ("x is 5.")
}
else
{
document.write ("x is not worth 5.")
}
document.write ("Out of the yew")

x = 5
if x == 5:
print ("x is 5.")
else:
print ("x is not worth 5.")
print ("Out of the yew")

4.1.3 Sophisticated version

If (C1), then (1st block of instructions), if not (C2), then (2nd block of instructions),
otherwise (3rd block of instructions). We can of course add other conditions "if not", this which does not change the scheme (except to extend it on the right).

Code JavaScript:-

if (condition1)
{
// code that will be executed if condition1 is true
}
else if (condition2)
{
// code that will be executed if condition1 is false
// and if condition2 is true
}
else
{
// code that will be executed when all the conditions
// previous are false
}

Code Python

if condition1:
## code that will be executed if condition1 is true
elif condition2:
## code that will be executed if condition1 is false
## and if condition2 is true
else:
## code that will be executed when all conditions
## previous are false

Example in JavaScript -

x = 5
if (x == 5)
{
document.write ("x is 5.")
}
else if (x == 6)
{
document.write ("x is 6.")
}
else
{
document.write ("x is neither 5 nor 6.")
}
document.write ("Out of the yew")

Example in Python -

x = 5
if x == 5:
print ("x is 5.")
elif x == 6:
print ("x is 6.")
else:
print ("x is neither 5 nor 6")
print ("Out of the yew")

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4.2 The loops

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The loops are used to execute several instructions a certain number of times,predefined or not.

4.2.1 The while command

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While means that. So the following command executes the code as long as the condition is true. If initially, the condition is false, then the code is not executed.

JavaScript Code -

while (condition) // mandatory parentheses
{
// code that will be executed as long as the condition is true
}

Python Code -

while condition: ## mandatory double-points
## code that will be executed as long as the condition is true
## this code must be indented (shifted right)
## as soon as the indentation stops, we leave the "while"

Example

In this example, we construct the sum of numbers from 1 to 10, excluding 10.

sum = 0
k = 1
while (k <10)
{
sum = sum + k
k = k + 1
}
document.write ("the sum is worth" + sum)

sum = 0
k = 1
while k <10:
sum = sum + k
k = k + 1
print ("the sum is worth", sum)

Tutorial Continued in next post...........

Thanks For Reading

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