How to display number with leading zeros in Python ?

To display numbers with leading zeros in Python, you can use string formatting techniques or the zfill() method. These methods work for integers, floats, and even negative numbers. Below are detailed explanations with examples:

1. Using F-Strings (Python 3.6+)

F-strings provide a concise and readable way to format numbers with leading zeros.

Example 1: Integer Padding

num = 7
formatted = f"{num:03d}"  # Pad to 3 digits with leading zeros
print(formatted)          # Output: "007"

Example 2: Float Padding

num = 3.14
formatted = f"{num:06.2f}"  # Pad to 6 characters (including decimal point)
print(formatted)             # Output: "003.14"

Example 3: Negative Numbers

num = -42
formatted = f"{num:04d}"  # Includes the negative sign in total width
print(formatted)           # Output: "-042"

2. Using `str.format()`

The format() method offers compatibility with older Python versions.

Example 4: Integer Padding

num = 25
formatted = "{:04d}".format(num)
print(formatted)  # Output: "0025"

Example 5: Float Padding

num = 5.5
formatted = "{:06.1f}".format(num)  # Pad to 6 characters
print(formatted)                     # Output: "0005.5"

3. Using `str.zfill()`

The zfill(width) method pads a numeric string with leading zeros.

Example 6: Basic Padding

num = 9
formatted = str(num).zfill(3)
print(formatted)  # Output: "009"

Example 7: Negative Numbers

num = -7
formatted = str(num).zfill(4)  # Negative sign counts toward total width
print(formatted)               # Output: "-007"

4. Using the `%` Operator

Legacy string formatting (similar to C’s printf).

Example 8: Integer Padding

num = 3
formatted = "%03d" % num
print(formatted)  # Output: "003"

Example 9: Float Padding

num = 2.718
formatted = "%06.2f" % num  # Pad to 6 characters
print(formatted)             # Output: "002.72"

Key Considerations

Negative Numbers:

F-strings and str.format() include the negative sign in the total width.
Example: f"{-5:03d}" → "-05".
To avoid this, use absolute values and re-add the sign:
python num = -5 formatted = f"-{abs(num):02d}" # Output: "-05"

Floats:

Specify total width and decimal precision (e.g., 06.2f means 6 total characters with 2 decimals).

Edge Cases:

If the number exceeds the specified width, it won’t be truncated:
python num = 1000 print(f"{num:03d}") # Output: "1000" (no truncation)

Comparison Table

Method	Syntax	Supports Floats?	Handles Negatives?	Best For
F-strings	`f"{num:03d}"`	Yes	Yes	Modern Python code
`str.format()`	`"{:03d}".format(num)`	Yes	Yes	Legacy compatibility
`zfill()`	`str(num).zfill(3)`	No (string only)	Yes (includes `-`)	Simple integer padding
`%` Operator	`"%03d" % num`	Yes	Yes	Legacy codebases

Common Use Cases

Timestamps (e.g., 09:05):

   hours = 9
   minutes = 5
   print(f"{hours:02d}:{minutes:02d}")  # Output: "09:05"

File Naming (e.g., image_001.jpg):

   index = 1
   filename = f"image_{index:03d}.jpg"
   print(filename)  # Output: "image_001.jpg"

Fixed-Width Data Formats (e.g., IDs like "00123"):

   user_id = 123
   print(f"{user_id:05d}")  # Output: "00123"

Summary

Use f-strings for modern Python code (e.g., f"{num:03d}").
Use zfill() for quick integer padding (e.g., str(7).zfill(3) → "007").
For floats, combine width and precision (e.g., f"{5.5:06.1f}" → "0005.5").
Handle negatives carefully to avoid unexpected results.

Let me know if you need further clarification!