# 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'>
                >>>

                #4 Python Glossary: Operator

                Operators in python is symbol that can perform value or variable. Operator can execute math, logic, assignment, comparison et cetera operation and give result. Without operator, variable only, python is only store value. But, python have operators so it can make calculate and imitate human mind.

                There are various operators in python.

                • Arithmetic operator
                • comparison/ relational operator
                • assignment operator
                • logical operator
                • membership operator
                • Identity operator
                • presedence operator

                Arithmetic Operator

                Arithmetic operator takes two value or variable then performs a calculation on them. The math operation is for example : addition (+), subtraction (-), multiplication (*) , division (/), %modulus , exponentiation(**). There are basic mathematical operations.

                >>> #this is addition or plus
                >>> 3+5
                8
                >>> #this is substraction or minus
                >>> 10 - 3
                7
                >>> #this is multiply two operand (value or variable)  either side of the operator
                >>> 4 * 5
                20
                >>> #division divide first operand by second operand
                >>> 10 / 2
                5
                >>> # modulus divides and returns the value of the remainder.
                >>> 10%3
                1
                

                Comparison/ Relational Operator

                Comparison/ relational operators compare the values on two sides of the value or variable. For example, 4 < 2 (output = False). After we write a comparison between value /variable/operand, then Python program in run mode will tell whether an operand is greater than the other, lesser, equal, or a combination of those. Various comparison operators are ( ==, != , <>, >,<=, etc)

                >>> #Equal to (==) check whether first operand equal to the second
                >>> 5 == 5
                True
                >>> x = 10
                >>> x == 11
                False
                >>> # Not equal to (!=) will check whether first is not equal to the second
                >>> 3 != 1
                True
                >>> 5 != 5
                False

                Assignment Operator

                Assignment operators in Python assign the value to a variable. Assign variable that already has value to a variable is allowed. But we can not assign a variable that has no value to a variable. There are several assignment operators used in Python (=, +=, – = , *=, /= , etc.)

                Logical Operator

                Logical operators consist 3 operator: or, and, not. That are used for combined conditional statements are true or false. The ‘and’ operator return to True only if two side are True. The ‘or’ operator return to True if one or two side are True. The ‘not’ for True is False. The ‘not’ for False is True.

                Membership Operator

                Membership operator check whether some value is membership of lists. There are two membership operator in Python: ‘in’ and ‘not in’

                Identity Operator

                Identity operator check whether two object is same. There are two identity operator. There are ‘is’ and ‘not is’.

                Precedence operator

                Precedence operator avoids ambiguity. It determines which operators need to be evaluated first. Precedence operator consists of parenthesis or (). Then multiplication has a higher precedence than addition. 

                #3 Python Glossary : Variable

                We have not to find meaning every word in python code. Some of them is user-defined name variable. So their word is as the programmer like.

                If we write or read python script, variables often appear. A variable is a container that represents data that we know or we decide it later. in algebra, a variable is a symbol for a number we don’t know yet. It is usually a letter like x or y. In Python, the variable is represented numbers, word, and lists that we already assign or we will assign later.

                Compare to spreadsheet like excel, python variable is like cell. Cell is empty container that we can decide value later. Python variable is a reserved memory location. Variable is place that we can store values.

                Form of variable in python is:

                • user-defined alphabet or word. The programmer defines a variable name, so find reference of the word is not necessary. So, a programmer can define a variable: var1, dido, doli, bubu, this_is_variable, and so on.
                • a variable name has no spaces.
                • start with a letter or underscore. We can not write a variable that starts with numbers. So, this example that is allowed: yoyo1, y4_ya, y1yi, et cetera. This is the example that not allowed: 1ya, 2yoyo et cetera.
                • consist one or more under case letter, underscore and number. We can not put a number in the first alphabet, but we can put it in a second or more position. For example my_variable, energy_var1, and so on.
                • Some of the words are python word that has specifics function. So we can not use 33 python keywords as a variable. They have another use in python. Python 33 keywords is : False. class, finally, is, return, None, continue, for, lambda, try, True, def, from, nonlocal, while, and, del, global, not, with, as, elif, if, or, yield, assert, else, import, pass, break, except, in, raise.
                • we can assign variable by using “=”. For example my_variable = 10
                • a variable is unique. We can not have two variables that have the same name. Python read it as same variable. Python read last statement as a valid value of the variable. You can see the example below.
                >>> my_variable = 10
                >>> print my_variable
                10
                >>> my_variable = 11
                >>> print my_variable
                11
                • A variable can contain number, text (string), or list (set of data).
                • To assign text to a variable, we have to give quotation mark before and after text.
                • We can assign variable with set of data list. For example, we have a variable that has named my_book. It can contain a set of data.
                >>> my_book =['python for beginner', 'dive to python', 'business']
                >>> my_text_variable = 'it is text'