Refresher: Functions¶

Recap¶

DRY RUN - Running code line by line, we run the code just like the compiler does without using human intelligence.
Loops - instead of writing the code multiple times, we use loops to perform the same task
Nested Loops - These are loops inside loops.
We usually use i for rows and j for columns.

QUIZ 1¶

What will the sequence be generated by the following?

range(-5,0,1)

Choices¶

-5,-4,-3,-2,-1,0
Nothing
0,-1,-2,-3,-4,-5
-5,-4,-3,-2,-1

QUIZ 2¶

What will the sequence be generated by the following?

range(-10,-5,-1)

Choices¶

-10,-9,-8,-7,-6,-5
-10,-9,-8,-7,-6
Nothing
-6,-7,-8,-9,-10

QUIZ 3¶

What will be the output of the following?

for i in range(1,10): 
    if(i % 3 == 0): 
        break
    print(i, end = ' ')

Choices¶

1 2 3 4 5 6 7 8 9
1 2
1 2 4 5 7 8 9
1 2 4 5 6 7 8

QUIZ 4¶

What will be the output of the following?

for i in range(0,4):
    for j in range(0,i):
        print('a', end = '')
    print()

Choices¶

a
aa
aaa
aaaa
aaaa
aaaa
aaaa
aaa
aa
a

Need for functions¶

We are working at a banking facility. We are to code the receipt that is printed after the ATM transaction. It is something like:

******************
Transaction Complete
Thank you for visiting
******************

so we will write the code for this:

print('*' * 5)
print("Transaction complete")
print("Thank you for visiting")
print('*' * 5)

Now for every type of transaction same message will be printed. And for every transaction contained in the big file of 10000 lines of code, we have the same 4 lines for different transactions.
This is not following the DRY(Do not repeat yourself) principle. Which is a bad practice.
Let us say the back says they don't want to print thank you they wish to print thanks instead. So we will have to update it at all the places separately.
Functions are like alias - I can write a line of code and I can name it abc. Everywhere I can call abc the same piece of code will be executed.
Functions make code modular.
Now if there are any changes, we change it in one place and it will reflect in all the other places.

Syntax of Defining a Function¶

Defining a function

def function_name():
    # actions

To Call the function

function_name()

The naming convention for a function is the same as variables.
- It should be composed of alphabet, number, and underscore
- should start with an alphabet or underscore
- It should not be a keyword
In Python we use snake case. (there are two cases camel case and snake case).

Return Statement¶

Functions not only put some code in a block they return something.

Example function

def area_circle_rad_5(){
    print(3.14 * 5 * 5)
}
area_circle_rad_5()

Output

78.5

This is how we define a function and call it. Now we want to add 1 to it or 2 to it. Can't we take it to a variable?
This is what return statements are for. It is like a black box where you want some task to be done. But after the task is done you want it to return some value as well.
So the syntax is something like:`

def function_name():
    return 5;

abc()
a = abc()
print(a)

Output

We are storing the return value of the function in a variable a. Now we can print this variable as usual.
Unlike other programming languages in Python we are not required to define the return type with the function name.

Note: Functions execution ends at return. Once a return statement is found rest of the lines of the code will not be executed. It is just like a break in loops. If you do return without any value, it will return None.

def abc():
    return
abc()

Parameter and Argument in Function¶

Let us say we want to calculate the area of a circle whose radius 10. We will again write the code as
```
def area_circle_rad_10():
    print(3.14 * 10 * 10)
```
So for every different radius we will write a different code? This is not a good practice.
In Python we can take as many parameters as required. So we can simply take radius as a parameter from the use.
```
def area_circle(radius):
    return (3.14 * (radius ** 2))

area = area_circle(5) 
```
If you want multiple parameters you can simply separate them by comma, their types are not required.
If the function is not returning anything by default it will return None.
In Python, a parameter is a variable used in a function definition, while an argument is an actual value passed to the function during a call.
About the above function radius used in the area_circle() function is a parameter, the 5 passed to it while calling is an argument.
But people use it interchangeably.

Execution of A Function in Python¶

Python compiler executes line-by-line
Everything in Python is an object of a class.
Function is also a class.
Function is just like a variable, a variable gets declared in a single line, and functions get declared in multiple lines.
In Python if you call a function without defining it, it will show an error.
We can call a function inside a function.
Let us say we have a bank function to do transactions for saving accounts. We have multiple functions to check the balance, to execute the transaction, to print the thank you message, etc.

Scope of a Variable¶

a = 1
def arae_circle(radius):
    area = 3.14 * (radius ** 2)
    return area
b = area_circle(10)
print(a)
print(area)
print(b)

Whatever we have done so far, we have done it in global scope.
Here a and b are global variables. But area is a local variable to the function area_circle. It can only be accessed in the function. As the execution of the function is over the Python compiler frees up the memory. Thus area is no longer a valid memory location.
Though we can do this:

a = 1
def arae_circle(radius):
    area = 3.14 * (radius ** 2)
    print(a)
    return area
b = area_circle(10)
print(a)
print(area) # this will give error
print(b)

This is because a is a global variable and can be accessed everywhere.

In Python variables defined in if or for loops can be used outside their block as well but it is not true for the functions.

a = 1
def abd():
    a = 2
    print(a)
abc()

Output

2
1

So, this will have two variables called a. One is global and another is local. When we say print(a) it will refer to the local variable and print its value.
To update or use global we use the following syntax:

a = 1
def abc():
    global a
    a = 2
    print(a)
abc()
print(a)

Output

2
2

Here global variable a is reused and its value is changed inside a function.

QUIZ 5¶

Is this a valid function?

def print_hello:
    print('Hello')

Choices¶

Yes
No

There are no paranthesis in the function and they are must in a function.

def print_hello():
    print('Hello')

¶

QUIZ 6¶

Is this a valid function?

def print_name():
    print('Hello', name)

Choices¶

Yes
No

The variable name must be taken as an argument.

QUIZ 7¶

How many times the function foo is called?

foo()
foo()
for i in range(1,5):
    foo()

Choices¶

5
6
7
8

QUIZ 8¶

What will be the output of the following?

def area_rectangle(l, b):
    area = l * b
area_circle(3, 4)
print(area)

Choices¶

12
7
Error

There is no function named area_cirle().

QUIZ 9¶

What will be the output of the following?

def foo(a):
    if(a):
        return 100
    a += 20
    return a
print(foo(0))

Choices¶

100
120
20
Nothing

A function's execution ends once a return is encountered.

If you do return without any value, it will return None. Though this is not helpful it is still valid.

def abc():
    return
abc()

QUIZ 10¶

What will be the output of the following?

def solve(a, b):
    print('Function Started')
    return 0
    c = a + b
    print('Function Ends')
c = solve(2, 3)
print(c)

Choices¶

Function Started
Function Ends
5
Function Started
Function Ends
0
Function Started
0
Function Ends
Function Started
0

We are doing early exit via return 0 and therefore the result is 0.

Positional and Keyword Arguments¶

Let us consider an example:

def bio_data(name, age, gender):
    print("Name: ", name)
    print("Age: ", age)
    print("Gender: ", gender)

bio_data(23, "Male", "Aakar")

`What is the problem with the above code?`¶

The order of the parameter matters, age will printed with the name, and so on
Python has two types of arguments Positonal and Keyword.
The above function call is referred to as positional arguments. Where order or position of arguments matters.
The other one is keyword argument. Here we have to give the name of the argument but the order doesn't matter.
The name must be the same as given in the function definition.
```
bio_data(name = "Aakar", gender = "Male", age = 23)
```

Note: A single call can have both together, but the Keyword argument must always be after positional arguments. Python will show an error if not done this way.

Cannot Do

bio_data("Aakar", age = 23, "Male")

Must Do

bio_data("Aakar", age = 23,gender = "Male")

Default and Non-default Arguments¶

Let us say we are writing the above function. For example, people don't like having to declare their gender. So, we can give the default argument gender with the value Unspecified in Python.

def bio_data(name, age, gender = "Unspecified"):
    print("Name: ", name)
    print("Age: ", age)
    print("Gender: ", gender)

bio_data(23, "Aakar")

Now, it is both ways okay even if we define or do not define the argument.

Note: A single call can have both together, but the Non-default argument must always be after default arguments. Python will show an error if not done this way.

Cannot Do

bio_data(name, age = 23, gender)

Must Do

def bio_data(name, age, gender = "Unspecified"):

QUIZ 11¶

What is the correct way of calling this function?

def print_biodata(name, age, gender):
    print('Name', name)
    print('Age', age)
    print('Gender', gender)

Choices¶

print_biodata('Hari', 'Male', 23)
print_biodata('Male', 'Hari', 23)
print_biodata('Hari', 23, 'Male')
print_biodata(23, 'Hari', 'Male')

QUIZ 12¶

What will be the output of the following?

def print_biodata(name, age = 23, gender = 'Female'):
    print('Name', name)
    print('Age', age)
    print('Gender', gender)

Choices¶

Yes
No

First there should be non-default arguments and then the default arguments.

QUIZ 13¶

Which of the function call is correct?

def print_biodata(name, age = 23, gender = 'Female'): 
    print('Name', name) 
    print('Age', age) 
    print('Gender', gender)

Choices¶

print_biodata(name='Hari', 23)
print_biodata('Hari', 23, age=23)
print_biodata('Hari')
print_biodata()
1^st option - name is a keyword argument and the age is a positional argument. Positional argument cannot come after keyword argument.
2^nd option - In the above quiz we are defining age twice which is not valid.
3^rd argument - Rest two arguments are default
4^th option - We still need name argument as name is not a default argument.
*args - opens a list/tuple (arguments)
**kwags - opens a dictionary (keyword arguments)
* is used for opening a single-dimension iterator.
Let us say there exists a function that takes an unspecified number of parameters.
This can be achieved with the help of *args and **kwargs. This lets us pass as many arguments as we want.

def abc(a, b, *args, **kwargs):
    print(a, b)
    print(args)
    print(kwargs)

abc(2,3,4,5, name = "Hari",age = 23)

Output

2 3
[4, 5]
{"name" : "Hari"
"age" : 23}

You cannot have more than one *args or **kwargs as their behavior of it is unspecified.

Docstrings¶

Python provides a special functionality doc strings just like comments but slightly different than multiline comments.
If someone wants to know how the function works they have to come to the code and see. So many Python code readers and default Python provides a documentation of functions and classes and these are called Doc String
You have to write a multiline comment right after the function definition.

def bio_data(name, age, gender = "Unspecified"):
    """
    This function prints the bio-data using the information provided

    Args:
        name
        age
        gender

    Returns:
        None
    """
    print("Name: ", name)
    print("Age: ", age)
    print("Gender: ", gender)

To read the doc string, just add a ? after it.

bio_data?

Question - Simple Interest¶

Take two parameters, how much they want to invest, and how long they want to invest it for.
Simple interest - 7%.
Write a function print_interest

si = 7
principal = int(input("How much you want to invest>"))
time = float(input("How long you want to invest it for (in years)?"))

def print_interest(principle, time):
    result = principle * time * si / 100
    return result

result = print_interest(principle, time)
print(result)

Question - Simple Interest¶

Round function in Python rounds the number. It takes the number and the precision we want. It rounds off this number and returns it.
```
round(3.1415,2) -> 3.14
```
Given a radius R, print the area of a circle but up to two decimal places only.

PI = 3.14159
def print_area(radius):
    area = PI * (radius ** 2)

result = print_area(5)
print(result)

Refresher: Functions¶

Recap¶

QUIZ 1¶

Choices¶

QUIZ 2¶

Choices¶

QUIZ 3¶

Choices¶

QUIZ 4¶

Choices¶

Need for functions¶

Syntax of Defining a Function¶

Return Statement¶

Parameter and Argument in Function¶

Execution of A Function in Python¶

Scope of a Variable¶

QUIZ 5¶

Choices¶

def print_hello(): print('Hello') ¶

QUIZ 6¶

Choices¶

QUIZ 7¶

Choices¶

QUIZ 8¶

Choices¶

QUIZ 9¶

Choices¶

QUIZ 10¶

Choices¶

Positional and Keyword Arguments¶

What is the problem with the above code?¶

Default and Non-default Arguments¶

QUIZ 11¶

Choices¶

QUIZ 12¶

Choices¶

QUIZ 13¶

Choices¶

Docstrings¶

Question - Simple Interest¶

Question - Simple Interest¶

`def print_hello(): print('Hello')`
¶

`What is the problem with the above code?`¶