🐍1.7Python String Slicing Explanation

Python String Slicing Explained (Using 'Divya')

Introduction to String Slicing

String slicing in Python allows you to extract a specific portion of a string using the syntax:

s[start:end:step]

• start: The index where slicing begins.
• end: The index where slicing stops (not included in the output).
• step: Defines the step size (positive for forward, negative for reverse).

For demonstration, let's take the string:

s = "Divya"

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Indexing Table

Index	D	i	v	y	a
Forward Index	0	1	2	3	4
Backward Index	-5	-4	-3	-2	-1

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1️⃣ Forward Slicing Cases

Case 1: s[1:-1:]

print(s[1:-1:])  # "ivy"

Breakdown:

• start = 1 → Starts from 'i'.
• end = -1 → Stops before 'a'.
• step = 1 (default) → Moves forward one character at a time.

✅ Result: "ivy"

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Case 2: s[0:3]

print(s[0:3])  # "Div"

Breakdown:

• start = 0 → Starts from 'D'.
• end = 3 → Stops before 'y'.

✅ Result: "Div"

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Case 3: s[:3] (Implicit Start)

print(s[:3])  # "Div"

Same as s[0:3] because start is omitted (defaults to 0).

✅ Result: "Div"

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Case 4: s[2:] (Implicit End)

print(s[2:])  # "vya"

• start = 2 → Starts from 'v'.
• end omitted → Runs until the end.

✅ Result: "vya"

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Case 5: s[::2] (Skipping Characters)

print(s[::2])  # "Dva"

• step = 2 → Takes every 2nd character.

✅ Result: "Dva"

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2️⃣ Reverse Slicing Cases

Case 6: s[::-1] (Reverse String)

print(s[::-1])  # "ayviD"

• step = -1 → Reads the string backward.

✅ Result: "ayviD"

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Case 7: s[1::-1]

print(s[1::-1])  # "iD"

Breakdown:

• start = 1 → Starts at 'i'.
• step = -1 → Moves backward.

✅ Result: "iD"

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Case 8: s[3:0:-1]

print(s[3:0:-1])  # "yvi"

Breakdown:

• start = 3 → Starts at 'y'.
• end = 0 → Stops before 'D'.
• step = -1 → Moves backward.

✅ Result: "yvi"

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Case 9: s[-1:-4:-1]

print(s[-1:-4:-1])  # "ayv"

• start = -1 → Starts at 'a'.
• end = -4 → Stops before 'D'.
• step = -1 → Moves backward.

✅ Result: "ayv"

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3️⃣ Edge Cases

Case 10: Empty Slice (s[3:3])

print(s[3:3])  # ""

Since start and end are the same, no characters are extracted. ✅ Result: ""

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Case 11: Out-of-Bounds (s[10:15])

print(s[10:15])  # ""

If indices are out of range, Python doesn't raise an error, it returns an empty string. ✅ Result: ""

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Summary Table

Expression	Result	Explanation
s[1:-1:]	"ivy"	Forward slice from 'i' to 'y', excluding 'a'.
s[1::-1]	"iD"	Reverse slice from 'i' to 'D'.
s[::-1]	"ayviD"	Full reverse string.
s[3:0:-1]	"yvi"	Backward slice from 'y' to 'i'.
s[-1:-4:-1]	"ayv"	Backward slice using negative indices.
s[:3]	"Div"	First three characters.
s[2:]	"vya"	Everything from 'v' onward.
s[::2]	"Dva"	Every second character.
s[3:3]	""	Empty slice.
s[10:15]	""	Out-of-bounds slice.

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Conclusion

String slicing is a powerful tool in Python that helps in extracting substrings efficiently. By understanding different slicing patterns, you can manipulate strings easily and write cleaner code.

I hope this guide clarifies all possible slicing cases! 🚀 Let me know if you have any questions. 😊