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Python ESO II AULA Cheat Sheet (DRAFT) by

Python comands for ESO II

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Basics

Spaces and indent­­ation (tabs) are relevant parts of the code
Instru­ctions in a block of code will have the same indent­ation
A block of code contains one or more lines of code inside it. The contained lines will be indented one more level than the container one.
A colon : opens a new block of code in the following line.
# at the beginning of a line marks this line as non-ex­ecu­table. For example
# This is a single line comment
To create multiple line comments, use three apostr­ophees in a row
'''
This is a
Multiline comment
'''

Variables

There's no declar­ation of variables. When you use a new name in an assign sentence, that becomes a variable of the type of the value assigned to it
a = 10 creates a variable called a that stores an integer value
The decimal separator is the point
a = 3.14 creates a variable called a that stores a decimal (float) value
To transform a numerical value into a string you cast it using the function str()
str(10) will create the string value "­10"
To transform a string value into an integer you cast it using the function int()
int("10­") will create the integer value 10
A variable contains a literal value of a certain type (integer, alphan­umeric, decimal, boolean, etc) and it can be used to perform different operations or construct logical expres­sions

Basic input / output

print(a)
Prints the content of the variable called a and opens a new line
print("Helo world")
Hello word
and opens a new line
print(a,end=",")
Prints the content of the variable called a and then a comma without opening a new line
print(name,end=",")
My name,
input()
Reads a string value form the keyboard
a = input() will store in a variable called a the value entered by the user as a string
int(in­put())
Reads a string value form the keyboard, ant casts it into an integer
a = int(in­put()) will store in a variable called a the value entered by the user casted as an integer

Flow control (more to be added along the course)

if (<expr>) :
Forks the execution stream according to the logical value of the expression <ex­pr>
if (a == b):
  <do something>
else:
As part of an if .. else block, starts the block code to be executed if the expresion was False
else:
  <do something esle>
elif (<expr2>):
Compound an else: statement with a new if statement
elif (a<b):
  <and another>
while (<expr>):
Generates a loop that will run as long as the expression <ex­pr> is True
while (a<10):
  <do something>
  <update a>
 

Arithmetic operators

+
add
12 + 5 returns 17
-
subtract
12 - 5 returns 7
*
product
12 * 5 returns 60
/
decimal division
12 / 5 returns 2.4
//
division (whole numbers)
12 // 5 returns 2
%
remainder of the division
12 % 5 returns 2
**
expone­nti­ation
12 ** 5 returns 248832

Comparison operators (logical)

<
less than
12 < 5 evaluates as False
<=
less than or equal to
12 <= 5 evaluates as False
==
equal to
12 == 5 evaluates as False
>=
greater than or equal to
12 >= 5 evaluates as True
>
greater than
12 > 5 evaluates as True
!=
not equal to
12 != 5 evaluates as True
In a compar­ison, the sign of equality (=) can never be alone as it would be confused with the assignment of values (a = 10). This is why the logical equality operator is a double sign of equality. Therefore a=10 means assign the value 10 to the variable a and a==10 means is the content of the variable a a number 10?

Lists

To be added next course

Maths

abs(arg)
receives an integer number as an argument and returns the integer absolute value
abs(-12) returns 12
math.fabs(arg)
receives a float as an argument and returns the float absolute value
math.f­abs­(-1­2.34) returns 12.34
math.f­abs­(-12) returns 12.0
math.f­loor(arg)
receives a float as an argument and rounds it down to the nearest integer
math.f­loo­r(2.5) returns 2
math.f­loo­r(-3.4) returns -4
math.ceil(arg)
receives a float as an argument and rounds it up to the nearest integer
math.c­eil­(2.5) returns 3
math.c­eil­(-3.4) returns -3
math.pi
returns the value of Pi
math.pi returns 3.1415­926­535­89793
You will need to import math

Logical operators

<expr1> and <expr2>
True if and only if the two expres­sions are True
(a>­0) and ­(a<5)
<expr1> or <expr2>
True if and only if at least one of the two expres­sions is True
(a<­0) or ­(a>=5)
not <expr>
True if and only if <ex­pre­ssi­on> is False
not ­(a==0)
By logical we understand an expression or operation that can only take two different values: True or False