How to generate a butterfly pattern using stars in Python

In this Answer, we will discuss how to generate a butterfly pattern using stars in Python.

Numerous patterns can be printed using Python, once we have a strong grip of the concepts involving loops. Here, we will use simple for loops to generate a butterfly pattern using stars.

Method 1

To create a butterfly pattern using Python programming, we will use two for loops:

  • First loop: It is used to form the upper two triangles (both right and left).
  • Second loop: It is used to form the lower two triangles (both right and left).

Code

Let’s look at the code snippet below.

# Number of rows
r = 5
# Upper Triangles
for i in range(1, r+1):
    print("*"*i, end="")
    print(" "*(r-i)*2, end="")
    print("*"*i)
# Lower Triangles
for i in range(r,0,-1):
    print("*"*i, end="")
    print(" "*(r-i)*2, end="")
    print("*"*i)

Explanation

  • Line 2 we took the input for half the number of rows, i.e., half the length of the wings of the butterfly.

  • Lines 5-8, we created a for loop to generate the upper triangles.

    • The print statement in line 6 generates the leftmost upper right-angled triangle.
    • The print statement in line 7 generates the spaces in between.
    • The print statement in line 8 generates the rightmost upper left-angled triangle.

  • Lines 11-14, we created a for loop to generate the lower triangles.

    • The print statement in line 12 generates the leftmost inverted right-angled triangle.
    • The print statement in line 13 generates the spaces in between.
    • The print statement in line 14 generates the rightmost inverted left-angled triangle.


Method 2

We can use a list comprehension to perform the above task.

  • We will use list comprehension to generate first half.

  • Then we will use the second list comprehension to generate the second half by reversing the first half.

Code

Let's look at the code below

def butterfly_pattern(rows):
    top_half = [
        f"{'*' * (i + 1)}{' ' * (2 * (rows - i - 1))}{'*' * (i + 1)}"
        for i in range(rows)
    ]
    bottom_half = top_half[::-1][1:]  
    pattern = top_half + bottom_half
    print("\n".join(pattern))
butterfly_pattern(5)

Explanation

  • Line 1: We create a function `butterfly_pattern(rows).

  • Line 2-4: We generate first half using list comprehension. It constructs the row by concatenating three parts: stars for the left half, spaces for the gap, and stars for the right half.

  • Line 6: I generates lower half by reversing the top_half.

  • Line 7-8: The top and bottom halves are concatenated and we print the pattern.

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