String slices

String slices

Python slicing is a sub-string of the given string from start to end.

The slice object is used to slice a given sequence (string, bytes, tuple, list or range) or any object which supports sequence protocol (implements __getitem__() and __len__() method).

slice() Constructor

The syntax of slice() :

• slice(stop)

·         slice(start, stop, step)

slice() Parameters

Three parameters:

• Start (optional) - where the slicing of the object starts. Default to none if not provided.
• Stop – Integer value until the slicing takes place. The slicing stops at index stop -1 (last element).
• Step (optional) - Integer value which determines the increment between each index for slicing. Defaults to none if not provided.

Return Type: Returns a sliced object containing elements in the given range only.

Index tracker for positive and negative index:
Negative comes into considers when tracking the string in reverse.

The operator [n : m] returns the part of the string from the “n-eth” character to the “m-eth” character, including the first but excluding the last. It help to the indices pointing between the characters.

If omit the first index (before the colon), the slice starts at the beginning of the string and If omit the second index, the slice goes to the end of the string:

>>> fruit = 'banana'

>>> fruit[:3]

'ban'

>>> fruit[3:]

'ana'

If the first index is greater than or equal to the second the result is an empty string, represented

by two quotation marks:

>>> fruit = 'banana'

>>> fruit[3:3]

'  '  An empty string contains no characters and has length 0, but other than that, it is the same

as any other string.

String ='ASTRING'    # Using slice constructor s1 = slice(3) s2 = slice(1, 5, 2)  s3 = slice(-1, -12, -2)    print("String slicing")  print(String[s1])  print(String[s2])  print(String[s3])

Output:

String slicing

AST

SR

GITA

 

Example

String ='ASTRING'     # Prints string in reverse  print("\nReverse String") print(String[::-1])

Output:

Reverse String

GNIRTSA

s = 'HelloWorld'

reverse_str = s[::-1]

print(reverse_str)

Output: dlroWolleH

Examples:- Steps and negative index values.

s1 = s[2:8:2]

print(s1)

Output: loo

Here the substring contains characters from indexes 2,4 and 6.

s1 = s[8:1:-1]

print(s1)

Output: lroWoll

Here the index values are taken from end to start. The substring is made from indexes 1 to 7 from end to start.

s1 = s[8:1:-2]

print(s1)

Output: lool

Python slice works with negative indexes too, in that case, the start_pos is excluded and end_pos is included in the substring.

s1 = s[-4:-2]

print(s1)

Output: or

 

Example 1: Create a slice object for slicing

# contains indices (0, 1, 2)

result1 = slice(3)

print(result1)

# contains indices (1, 3)

result2 = slice(1, 5, 2)

print(slice(1, 5, 2))

Output

slice(None, 3, None)

slice(1, 5, 2)

---

Example 2: Get substring using slice object

# Program to get a substring from the given string 

py_string = 'Python'

# stop = 3

# contains 0, 1 and 2 indices

slice_object = slice(3) 

print(py_string[slice_object])  # Pyt

# start = 1, stop = 6, step = 2

# contains 1, 3 and 5 indices

slice_object = slice(1, 6, 2)

print(py_string[slice_object])   # yhn

Output

Pyt

yhn

---

Example 3: Get substring using negative index

py_string = 'Python'

# start = -1, stop = -4, step = -1

# contains indices -1, -2 and -3

slice_object = slice(-1, -4, -1)

print(py_string[slice_object])   # noh

Output

noh

---

Example 4: Get sublist and sub-tuple

py_list = ['P', 'y', 't', 'h', 'o', 'n']

py_tuple = ('P', 'y', 't', 'h', 'o', 'n')

# contains indices 0, 1 and 2

slice_object = slice(3)

print(py_list[slice_object]) # ['P', 'y', 't']

# contains indices 1 and 3

slice_object = slice(1, 5, 2)

print(py_tuple[slice_object]) # ('y', 'h')    

Output

['P', 'y', 't']

('y', 'h')

Example 5: Get sublist and sub-tuple using negative index

py_list = ['P', 'y', 't', 'h', 'o', 'n']

py_tuple = ('P', 'y', 't', 'h', 'o', 'n')

# contains indices -1, -2 and -3

slice_object = slice(-1, -4, -1) 

print(py_list[slice_object])  # ['n', 'o', 'h']

# contains indices -1 and -3

slice_object = slice(-1, -5, -2)

print(py_tuple[slice_object]) # ('n', 'h')

Output

['n', 'o', 'h']

('n', 'h')

Example 6: Using Indexing Syntax for Slicing

For example,

py_string = 'Python'

# contains indices 0, 1 and 2

print(py_string[0:3])  # Pyt

# contains indices 1 and 3

print(py_string[1:5:2]) # yh

Output

Pyt

yh

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