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Use an outer loop for the rows and an inner loop for the values in each row. This prints 1, then 12, then 123, continuing up to the number of rows you choose:
rows = 5
for row in range(1, rows + 1):
for value in range(1, row + 1):
print(value, end="")
print()1
12
123
1234
12345How the nested-loop solution works
range(1, rows + 1)makes the outer loop visit each row number from 1 throughrows.range(1, row + 1)makes the inner loop print values from 1 through the current row number. Python’srange()excludes its stop value, so adding 1 includes the row number. The Python 3.14.8 tutorial explains that the given endpoint is not part of the generated sequence.print(value, end="")keeps each value on the current line. The separateprint()after the inner loop ends that row and moves to the next line. The Python Guides pattern tutorial demonstrates this print-line-ending approach.
The outer loop controls how many rows appear; the inner loop controls the contents of each row. This makes nested for loops a clear starting point for learning the pattern.
Five ways to create the pattern or a close variation
1. Nested for loops
This is the direct version: each row prints the integers from 1 through its row number.
rows = 5
for row in range(1, rows + 1):
for value in range(1, row + 1):
print(value, end="")
print()2. Nested while loops
A while loop produces the same output, but you must initialize and increment each counter yourself. Reset the inner counter at the beginning of every row.
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rows = 5
row = 1
while row <= rows:
value = 1
while value <= row:
print(value, end="")
value += 1
print()
row += 13. Build each row as a string, then print it
This separates constructing a row from displaying it. The generator converts each number to text, and join() combines those pieces without a separator.
rows = 5
for row in range(1, rows + 1):
line = "".join(str(value) for value in range(1, row + 1))
print(line)4. Use a comprehension to build each row
This compact form uses a generator expression inside join(). It has the same row bounds as the string-building version, but puts the row construction in one expression.
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rows = 5
for row in range(1, rows + 1):
print("".join(str(value) for value in range(1, row + 1)))5. Multiply a string for a repeated-digit pattern
This is a related pattern, not the original counting sequence. Multiplying the row number as text repeats that digit the required number of times, giving 1, 22, 333, and so on.
rows = 5
for row in range(1, rows + 1):
print(str(row) * row)Eight more number and character patterns
Each example changes either the loop bounds or the expression used to build a row. These are variations on the exercise: some keep the same growing triangle shape, while others change the values, spacing, or alignment.
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1. Repeat the row number
Output:
1
22
333
4444
55555Repeat the current row number instead of counting upward inside each row.
rows = 5
for row in range(1, rows + 1):
print(str(row) * row)2. Print rows in descending length
Output:
12345
1234
123
12
1Start the outer loop at the maximum row length and count down; the inner loop still counts upward from 1.
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rows = 5
for row in range(rows, 0, -1):
print("".join(str(value) for value in range(1, row + 1)))3. Count downward within each row
Output:
1
21
321
4321
54321Make the inner loop count from the current row down to 1.
rows = 5
for row in range(1, rows + 1):
print("".join(str(value) for value in range(row, 0, -1)))4. Separate values with spaces
Output:
1
1 2
1 2 3
1 2 3 4
1 2 3 4 5Give join() a space separator instead of an empty string.
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rows = 5
for row in range(1, rows + 1):
print(" ".join(str(value) for value in range(1, row + 1)))5. Print an asterisk triangle
Output:
*
**
***
****
*****Repeat an asterisk once for each position in the row.
rows = 5
for row in range(1, rows + 1):
print("*" * row)6. Continue counting across rows
Output:
1
23
456
78910
1112131415Keep a counter outside both loops so it does not reset to 1 at the start of a new row.
rows = 5
value = 1
for row in range(1, rows + 1):
for _ in range(row):
print(value, end="")
value += 1
print()7. Center a number pyramid
Output:
1
121
12321
1234321
123454321For each row, print leading spaces to shift the values toward the center. Build the ascending half, then append the descending values without repeating the peak.
rows = 5
for row in range(1, rows + 1):
ascending = "".join(str(value) for value in range(1, row + 1))
descending = "".join(str(value) for value in range(row - 1, 0, -1))
print(" " * (rows - row) + ascending + descending)8. Count up, then back down
Output:
1
121
12321
1234321
123454321Join an ascending sequence with a descending sequence that starts one below the row number, so the peak appears only once.
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for row in range(1, rows + 1):
ascending = "".join(str(value) for value in range(1, row + 1))
descending = "".join(str(value) for value in range(row - 1, 0, -1))
print(ascending + descending)Which method should you use?
| Method | Best fit | What to keep in mind |
|---|---|---|
Nested for loops |
Learning how row and value loops work | The loop bounds make each printed value explicit. |
Nested while loops |
Practicing counters and loop conditions | Initialize and increment both counters correctly. |
| Build a row string | Separating row construction from output | Convert numbers to strings before joining them. |
Comprehension with join() |
Writing a compact row expression | It is shorter, but the nested-loop version makes the iteration easier to inspect. |
| String multiplication | Repeating one character or digit | It creates a different pattern from the ascending number triangle. |
Common mistakes
- Leaving out the final value:
range()excludes its stop argument. Userow + 1when the current row number must be included. - Starting a new line after every value: the default
print()ends with a newline. Useend=""while printing a row, then callprint()once after that row. - Not resetting a
whileloop’s inner counter: set the value counter back to 1 at the beginning of each row, or later rows will have no values to print. - Confusing repeated digits with counting rows:
str(row) * rowrepeats the row digit; use an inner loop or joined range to print the values 1 through the row number.
Source note
The official Python 3.14.8 control-flow tutorial documents the exclusive stop value for range(). A direct nested-loop triangle example also appears in Python Guides and in Waterside Code Club’s Python From Zero To One. The string-building, comprehension, and pattern-variation examples above are coding alternatives derived from the loop and string operations shown here, not performance comparisons.
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