Conditions and Loops in Python
Tags: python, tutorial, beginners, programming
Published: 2022-09-13 13:02:24

What if you want to do some specific tasks when the string is "Python" and some other tasks when the string is "Java". To achieve this conditioning we can use conditional statements in python or any other language. When we want to do some task for n number of times or we want to loop through some specific list, we can use different types of loops in this kind of situation.

# Conditional Statements in Python

In python, we have two types of conditional statements.

1. If-else
2. if-elif-else (if - else if - else)

Both conditional statements seem almost similar, and actually, they are. There is just a minor difference between these two statements. We will understand this difference using code examples. If you know any other language(s), you might be wondering if python has a switch case or not. NO, python does not have a switch case.

## if-else

Syntax:

```python
if(conditional expresson):
	statement
else:
	statement
```

If I have explained the if-else statement in plain English then it would be the "either this or that" statement.

Let's assume if the string is **java**, I want to do the sum of two numbers else I want to multiply two numbers.

```python
num1 = 5
num2 = 2

lang = 'java'

if(lang=="java"): # check if value of lang variable is 'java'
    c = num1 + num2
    print(c)
else:
    c = num1 * num2
    print(c)

# OUTPUT: 7
```

```python
num1 = 5
num2 = 2

lang = 'java'

if(lang!="java"): # check if value of lang variable is NOT 'java'
    c = num1 + num2
    print(c)
else:
    c = num1 * num2
    print(c)

# OUTPUT: 10
```

It is not compulsory to use else part. You can use only if part as well. For example, add the string "Programming" to the existing string if it is "Python" or does nothing.

```python
lang = 'Python'

if(lang=="Python"):
    lang = lang +" Programming"

print(lang)
# Output: Python Programming


lang = 'Java'

if(lang=="Python"):
    lang = lang +" Programming"

print(lang)
# Output: Java
```

Sometimes, you can go into the if statement using only variable as well. For example,

```python
lang = 'Python'
if(0):
    lang = lang +" Programming"
print(lang)
# OUTPUT: Python

lang = 'Python'
if(1):
    lang = lang +" Programming"
print(lang)
# OUTPUT: Python Programming

lang = 'Python'
if(True):
    lang = lang +" Programming"
print(lang)
# OUTPUT: Python Programming

lang = 'Python'
if(False):
    lang = lang +" Programming"
print(lang)
# OUTPUT: Python

lang = 'Python'
if(""):
    lang = lang +" Programming"
print(lang)
# OUTPUT: Python

lang = 'Python'
if("random string"):
    lang = lang +" Programming"
print(lang)
# OUTPUT: Python Programming

lang = 'Python'
if(None):
    lang = lang +" Programming"
print(lang)
# OUTPUT: Python

lang = 'Python'
if([1]):
    lang = lang +" Programming"
print(lang)
# OUTPUT: Python Programming

lang = 'Python'
if([]):
    lang = lang +" Programming"
print(lang)
# OUTPUT: Python

lang = 'Python'
if({'a':1}):
    lang = lang +" Programming"
print(lang)
# OUTPUT: Python Programming

lang = 'Python'
if({}):
    lang = lang +" Programming"
print(lang)
# OUTPUT: Python
```

If we want to combine multiple conditions we can use **_and_** and **_or_** within the if statement.

```python
lang = 'PYTHON'

if(lang.isupper() and len(lang) > 2):
    print("Worked!")
# OUTPUT: Worked!

if(lang.islower() or len(lang) == 6):
    print("Worked again!")
# OUPUT: Worked again!
```

## if-elif-else

Syntax:

```python
if(conditional expresson):
	statement
elif(conditional expresson):
	statement
else:
	statement
```

We use this conditional statement when we want to test more than one scenario. Let's understand this by an example.

```python
marks = 75

if(marks >= 34 and marks <= 50):
    print("Grade C!")
elif(marks > 50 and marks <= 75):
    print("Grade B!")
elif(marks > 75 and marks <= 100):
    print("Grade A!")
elif(marks >= 0 and marks < 34):
    print("FAIL!")
else:
    print("Something is wrong!")

# OUTPUT: Grade A!
```

Be aware when you use multiple **_if_** and **_if-elif_**. A single error in your logic and all your code-base can throw an error. To understand this, see the below example.

```python
marks = 75

if(marks > 75 and marks <= 100):
    print("Grade A!")
elif(marks > 50):
    print("Grade B!")
elif(marks >=34):
    print("Grade C!")
else:
    print("Something is wrong!")

print("-----------------------------------")

marks = 75

if(marks > 75 and marks <= 100):
    print("Grade A!")
if(marks > 50):
    print("Grade B!")
if(marks >=34):
    print("Grade C!")

"""	OUTPUT:
Grade B!
-----------------------------------
Grade B!
Grade C!
"""
```

# Loops in Python

In python, we have two kinds of loops.

1. for Loop
2. while Loop
3. Loop Control Statements

## for Loop in Python

Syntax:

```python
for iterator in sequence:
    statement(s)
```

For loop is used when we want to traverse through the sequential datatype. For example traversing through lists, tuples, strings etc.

```python
fruits = ['apple', 'banana', 'mango', 'grapes', 'peach']

for fruit in fruits:
    print(fruit)

""" OUTPUT:
apple
banana
mango
grapes
peach
"""

for i in range(len(fruits)):
    print(fruits[I])

""" OUTPUT:
apple
banana
mango
grapes
peach
"""
```

In the first example above, in the _fruit_ variable, we are directly getting each element of the _fruits list_. Whereas, in the second example, we are accessing each element by index reference. The range(n) function returns a sequence of numbers.
Syntax: `range(start, stop, step)`.

```python
for i in range(2, 13, 3):
    print(i)

""" OUTPUT:
2
5
8
11
"""
```

We can use for loop with dictionaries as well.

```python
dict1 = {"lang": "python", "year": "2021", "month": "november"}

for item in dict1:
    print(item, ":" , dict1[item])

""" OUTPUT:
lang : python
year : 2021
month : november
"""
```

## while Loop in Python

Syntax:

```python
while expression:
    statement(s)
```

When you need to do some work repeatedly until some condition satisfies, in that situation you can use a while loop.

Let's assume we need to print "Hello World" until the count variable became 5.

```python
count = 0
while (count < 5):
    print("Hello World")
    count = count + 1
```

# Loop Control Statements

There are times when you need to break the loop or skip some iterations in the loop or do nothing. This kind of thing can be done using Loop Control Statements. In python, we have three looping control statements.

1. Break statement
2. Continue statement
3. Pass statement

We use a break statement when we want to break the loop when certain conditions match. For example,

```python
fruits = ['apple', 'banana', 'mango', 'grapes', 'peach']

for fruit in fruits:
    if(fruit == 'mango'):
        break
    print(fruit)

""" OUTPUT:
apple
banana
"""
```

While the break statement breaks the loop, the continue statement makes the loop skip the current iteration and forces it to go to the next iteration.

```python
fruits = ['apple', 'banana', 'mango', 'grapes', 'peach']

for fruit in fruits:
    if(fruit == 'mango'):
        continue
    print(fruit)

""" OUTPUT:
apple
banana
grapes
peach
"""
```

Pass statement is a meaningless piece of code that suggests the interpreter to do nothing. It is similar to the comment but comments are ignored by interpreters while the pass statement executed by the interpreter and as per the name does nothing. Pass statement is used with function and class as well, which I will explain in the next section.

```python
fruits = ['apple', 'banana', 'mango', 'grapes', 'peach']

for fruit in fruits:
    if(fruit == 'mango'):
        pass
    print(fruit)

""" OUTPUT:
apple
banana
mango
grapes
peach
"""
```

# for...else & while...else

During the development journey, there are times when you might need to use for..else and while...else. These are just normal for and while loop with special else cases. Let's see an example to understand it.

```python
fruits = ['apple', 'banana', 'mango', 'grapes', 'peach']

for fruit in fruits:
    if(fruit == 'mango'):
        break
    print(fruit)
else:
    print("Loop Did Not Break!")

""" OUTPUT:
apple
banana
"""
```

```python
fruits = ['apple', 'banana', 'mango', 'grapes', 'peach']

for fruit in fruits:
    if(fruit == 'abc'):
        break
    print(fruit)
else:
    print("Loop Did Not Break!")

""" OUTPUT:
apple
banana
mango
grapes
peach
Loop Did Not Break!
"""
```

So, you might have guessed. When the loop does not break OR the loop completes all the iterations without interruption, else block is executed. The same happens with the while loop as well.

```python
i = 1
while i < 6:
  if(i == 3):
    break
  print(i)
  i += 1
else:
  print("All iterations of While are executed successfully.")

""" OUTPUT:
1
2
"""
```

# Conclusion

Finally! We are at the end of this section 😁.

I know, it is a lot to take in at a time. But, you don't need to remember everything that I have mentioned here. I just showed you so that you can recall what is possible and what is not. There are some other methods as well that I have not mentioned here.

If you want to find out more about control statements and loops in python, check out [Programiz](https://www.programiz.com/python-programming/if-elif-else).

---

That was it. Thank you for reading.

Make sure to share any thoughts, questions, or concerns. Let me know if you need any help or want to discuss something. Reach out to me on [Twitter](https://twitter.com/sahil_fruitwala) or [LinkedIn](https://www.linkedin.com/in/sahilfruitwala). Make sure to share any thoughts, questions, or concerns. I would love to see them.

Till the next time 👋