#8 Loop Statement in Python

Loop statement in Python executes repeatedly the statement as long as a given condition is true. A unique feature of loop statement is repetition.

Loop and conditional statement have the similar and different point. Different than a conditional statement, the loop statement will repeat if match the condition. Similar to the conditional statement, the loop statement has a condition to execute. Sometimes, the programmer said it repetition structure or iteration.

The Syntax of Loop Statement

Syntax of loop statement is

>>> while condition :
        statement #if meet condition

The statement will repeat if condition is true.

#7 Conditional Statement in Python

Why Auto driver that python makes can make an adjustment to an unpredictable situation. For example, if a car faces another stopped car in front of it, the auto driver can also stop accordingly. That is amazing.

Python can do that, because python have conditional statement or If statement.

The conditional statement is useful for creating a decision structure. Decision depends on condition. This allows a program to create more than one scenario. The if statement has an instruction for one ,, and another different instruction for another condition.

If statement have component, boolean and relational expression to check condition. Beside that, this if statement also have instruction to execute if condition as request.

Boolean and Relational Expression

A Boolean value has two value, True or False. Statement that use this value is Check Statement. Check Statement is statement that evaluate whether the statement true or false. In English language, is A is same with B? in Python language, A==B. faces statement tests an expression to determine whether it is true or false.
Boolean value is named after George Boole formulate some rules for reasoning about and combining this binary value (True and False). It is suit for computer that have binary value, 0 and 1.


We can get list of boolean value in Python by type : dir(True).

>>> dir(True)
       ['abs', 'add', 'and', 'class', 'cmp', 'coerce', 'delattr', 'div', 'divmod', 'doc', 'float', 'floordiv', 'format', 'getattribute', 'getnewargs', 'hash', 'hex', 'index',
       'init', 'int', 'invert', 'long', 'lshift', 'mod', 'mul', 'neg', 'new', 'nonzero', 'oct', 'or', 'pos', 'pow', 'radd', 'rand', 'rdiv', 'rdivmod', 'reduce', 'reduce_ ex', 'repr', 'rfloordiv', 'rlshift', 'rmod', 'rmul', 'ror', 'rpow', 'rrshift', 'rshift', 'rsub', 'rtruediv', 'rxor', 'setattr', 'sizeof', 'str', 'sub', 'subclasshook', '_
       truediv_', 'trunc', 'xor', 'bit_length', 'conjugate', 'denominator', 'imag', 'numerator', 'real'] "
      

That is a list of several function related to boolean type data.

Another alternative, we can read the documentation by type “help(True) ” or “help(False) in python command line.

>>> help(True)
       Help on bool object:class bool(int)
  |  bool(x) -> bool
  |
  |  Returns True when the argument x is true, False otherwise.
  |  The builtins True and False are the only two instances of the class bool.
  |  The class bool is a subclass of the class int, and cannot be subclassed.
  |
  |  Method resolution order:
  |      bool
  |      int
  |      object"
...
 l

Usually, Boolean operator use equal (==), greater(>) and less to determine whether a specific relationship True or False.

SymbolMeaning
> Greater than
>= Greater than or equal to
< Less than
<=Less than or equal to
== Equal to
!=Not equal to

Boolean Value in Conditional Expression

How boolean value in conditional expression. In Python language, the syntax of Conditional is like this

>>> If condition :
       statement

Condition in the syntax is boolean statement. That is something that computer can evaluate whether that is True or False. True or False in the term of meet condition. That is not about morality or epistemology.

In flowchart, Conditional Statement use symbol like this.

Logical Operator


Python also accommodate more complicated expression in boolean mode. There are logical operator to combine simpler boolean operator. The logical operator is” and”, “or” and “not”.

“and” Operator


The and and or combine two boolean expression. “And” operator evaluate expression as true only if the both expression is true. The truth table is like this.

XYX and Y
TrueTrueTrue
TrueFalseFalse
FalseTrueFalse
FalseFalseFalse

“or” Operator

or operator evaluate two statement. Then if one or more statement is true, the or operator return to True.

XYX or Y
TrueTrueTrue
TrueFalseTrue
FalseTrueTrue
FalseFalseFalse

“not” Operator

not operator can apply to one statement or more.
if the not operator apply to True value, it flowcharts to False.

Xnot X
TrueFalse
FalseTrue

Conditional Execution

A conditional statement has a ability to check condition and execute instruction or statement based on condition.
The syntax is like below.

>>> if True: # This is always True,
        pass # so this is always executed, but it does nothing
>>>  else:
        pass"

Chained conditionals/ nested decision

if we need more than two condition and more than two instruction, python also accommodate. Chained or nested decision structure check more than one condition.

Notation of chained conditional statement is like this.


That is the conditional statement inside another conditional statement.

# 6 Function in Python

Function is also the most used element in Python programming language. It is a sequence of statements. So, Function combine variable, data, and operator. The function is one of the most used element because it will reduce working time by reduce repeated statement and formula.

If we familiar about function in math and spreadsheet, you can understand easily.

The spreadsheet gives us a ready use function. For example average(A1:A10). This function will sum all numbers within A1:A10 cell, then divide it by count of numbers. Spreadsheet hide detail process of the average function. Only show name and its parameters. This will reduce complexity, and

In mathematics, a function show of how a varying quantity of variable depends on another quantity. … If the f is a name of function , the notation is y = f (x) (read f of x). Function will manipulate x based a formula.

Python has many functions. There are a built-in function in python, functions in modules, and we can make new Built-in.

Built-in Function

A built-in function is a function that Python already provides if we install it. We can see the built-in function here.

Then, to call built-in function is simple. Syntax of built-in function is functionname(parameter). Example, we use the sum function below.

>>> x =[2,4,5,6]
>>> sum(x)
17
>>> len(x)
4

len(parameter)” is also built-in function in python. It mean quantity of data series.

Function in Standard Library

Python also has a hidden function at modules in the standard library folder. We have to call its modules to use it. This is example to use random modules

>>> import random
>>> random.randint(0, 20)
7
>>> random.randint(500, 50000)
18601

We can read the notation is randit function of (0,20) in the ‘random’ modules. Random module have randint function, or random integer.

This is list of modules standard libray.

  • os
  • shutil
  • glob
  • sys
  • re
  • math
  • urllib2
  • smtplib
  • date
  • zlib
  • Timer
  • unittest

Third Party Library

As I talk in the introduction, Python have big community. They create tons of library and always growing. We can use their modules by install them previously. It is website that store library by community: https://pypi.org. To install them, we can go to command prompt or terminal.

pip install modulename

After install third party modules successfully, we can import to use it.

import modulename

modulename is name of modules that you want to install. Dont type module name. If you install BeautifulSoup modules, you can type pip install BeautifulSoup

pip install BeautifulSoup

User Defined Function

If we want to make our own function, we can make it in python.

Syntax to create our create from scratch function is:

def NAME( PARAMETERS ):
STATEMENTS

For example, if we want to create average function. We can make function like in code below.

>>>def average(xx):
       av = sum(xx)/len(xx)
       return av
y = [1,2,3,4,5]
print average(y)

That is example of user-defined function.

# 5 Data Type in Python Language

Python programmers often have problem with their script. Their script cannot run well, often because of the incorrect data type. Some of the different data types can not work in one operation and python give error result.

In this article, we will show 5 data type in python. Python has five standard Data Types.

The Python data types are: numbers, strings, list, tuple, and dictionary.

  1. Numbers
    1. Integer
      1. Float Point Number
        1. Complex Number
        2. Strings
          1. List
            1. Tuple
              1. Dictionary

                This is something that every programmer need to know. It help us to prevent error and make dream program into reality.
                After reading this article, you can prevent error that stop program. You can also imagine more about what program can do. There
                First, let’s talk about numbers

                Numbers

                “The most used number data type is integer and floating. But that is not the only number data type in python. Python has another number data type. There is complex, decimals and fractions.

                Integer

                Integer is the whole number without fractional number. It includes positive, negative and zero number. But it does not include 1.5, because that is a fractional number. 50% is not an integer because it is a fractional number. Example of integer is -60, 31, 0, 50 38. and so on.
                If we assign integer number to a variable, python automatically defines its number and variable as an integer.
                In Python programming language, declaration data as number is simple. Write a variable and assign a number without punctuation.
                This is an example. Var1 = 23. This is make var1 as number integer data type. Yo can check the type of variable by writing “type(var)” in python.

                >>> var = 34
                >>> type(var)
                <type 'int'>

                Float Point Number

                Float point number is fractional number or decimal number. The fractional part or decimal part of a non‚Äźnegative real number is the excess beyond that number’s integer part. For example 0.1, 5.1.
                In python, to define that some variable as float type, we just assign float point number to a variable. For example, we have variable C and data float point, 1.3.

                >>> c= 1.3 # dot in this number is sign of decimal number after dot.
                >>> type(c)
                <type 'float'>

                It is possible in python to make mathematic operatation between float and integer. For example

                >>> c= 1.3
                >>> type(c)
                <type 'float'>
                >>> d = 29
                >>> type(d)
                <type 'int'>
                >>> w = c+d
                >>> w
                30.3
                >>> type(w)
                <type 'float'>       

                Python support operand type(s) for float and integer.

                Complex Number

                Complex number is a combination of real number and imaginative number. The syntax of complex number is , + j. We has to add “j” to imaginary part. Example

                >>> 3+6j
                (3+6j)"

                Strings


                strings are sequences of alphabet, text, or number data. It is character data. Number as character data different than gives integer. If we assign number as character data, we can not make mathematic operation correctly.

                To make python understand, that some data is strings is by add quote or double quote befor and after data. The data is include

                This is example number as character data.

                >>> x = '9'  #
                >>> type(x)
                <type 'str'>
                >>> x *5
                '99999'

                The example show that ‘9’ * 5 (‘9’ multiply 5) is not 45, but ‘99999’. Because, the ‘9’ is not integer, but string.

                If the between string and integer is allowed, python cannot do the addition for them. It is example. Python give error message.

                >>> x = '8'
                >>> x*4
                '8888'
                >>> x +5
                Traceback (most recent call last):
                  File "<stdin>", line 1, in <module>
                TypeError: cannot concatenate 'str' and 'int' objects
                >>>

                List

                A variable can have more than one data or lists. Python have 3 distinct lists. There are: list, tuple, and dictionary. In this section we talk about list.

                List is a collection of values. It is series of values. Data type of values can be number or strings. List variables are declared by using brackets  “[” and “]” following the variable name. See distinct of {}, (), and [] carefully.

                Tuple is also collection of values. Unique feature of list compare to tuple is mutable. We change the member of list easily.

                your_list = [2,3,4,5,6]
                my_list = ["we', "are", "champion"]
                empty_list = []

                Python give index of every member of list. The index is start with 0. There are 0,1,2,3 and so on. So we can also retrieve the list by its index number. For example.

                >>> ere = ["yes", 90, "wow"]
                >>> ere[0]
                'yes'
                >>> ere[2]
                'wow'

                List can be member of another list.

                >>> ere = ["yes", 90, "wow"]
                >>> newlist = [ere, [3,5,"5"]]
                >>> newlist
                [['yes', 90, 'wow'], [3, 5, '5']]
                >>>

                We can retrieve list in the list by two bracket square.

                >>> newlist
                [['yes', 90, 'wow'], [3, 5, '5']]
                >>> newlist[0][1]
                90
                >>>

                Tuple

                Tuple is also collection of value. Different than list data type, tuple data type immutable. We can not change its member easily.

                It is simple to create a tuple. We can type colletion of value within parenthesis ().

                >>> mytuple=(1,2,"three")
                >>> type(mytuple)
                <type 'tuple'>
                >>>
                

                Dictionary

                Dictionary is also a collection of value. But different than list and tuple, dictionary, the values of dictionary are pair of key and value. Imagine about an english german dictionary. The list have pair of english word and its meaning in germany language.

                 eng2g = {"one": "eins", "two": "zwei", "three": "drei"}

                To declare a variable as dictionary is simple. If list have bracket square [], tuple have parenthesis (), dictionary have {}. The pair of value have :

                >>> gg ={}
                >>> type(gg)
                <type 'dict'>
                >>>