Python string supports slicing to create substring. Note that Python string is immutable, slicing creates a new substring from the source string and original string remains unchanged.
Python slice string
Python slice string syntax is:
str_object[start_pos:end_pos:step]The slicing starts with the start_pos index (included) and ends at end_pos index (excluded). The step parameter is used to specify the steps to take from start to end index. Python String slicing always follows this rule: s[:i] + s[i:] == s for any index ‘i’. All these parameters are optional - start_pos default value is 0, the end_pos default value is the length of string and step default value is 1. Let’s look at some simple examples of string slice function to create substring.
s = 'HelloWorld' print(s[:]) print(s[::])Output:
HelloWorld HelloWorldNote that since none of the slicing parameters were provided, the substring is equal to the original string. Let’s look at some more examples of slicing a string.
s = 'HelloWorld' first_five_chars = s[:5] print(first_five_chars) third_to_fifth_chars = s[2:5] print(third_to_fifth_chars)Output:
Hello lloNote that index value starts from 0, so start_pos 2 refers to the third character in the string.
Reverse a String using Slicing
We can reverse a string using slicing by providing the step value as -1.
s = 'HelloWorld' reverse_str = s[::-1] print(reverse_str)Output: dlroWolleH Let’s look at some other examples of using 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.
Output: lool
Output: or
That’s all for python string slice function to create substring.
You can checkout complete python script and more Python examples from our GitHub Repository.
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The
type object for slice objects. This is the same as slice in the Python layer. Return true if ob is a slice object; ob must not be NULL. This function always succeeds. Return a new slice object with the given values. The start, stop, and step parameters are used as the values of the slice object attributes of the same names. Any of the values may be NULL, in which case the None will be used for the corresponding attribute. Return NULL if the new object could not be allocated.
Part of the Stable ABI.
Return value: New reference. Part of the
Stable ABI.
Part of the Stable ABI.
Retrieve the start, stop and step indices from the slice object slice, assuming a sequence of length length. Treats indices greater than length as errors.
Returns 0 on success and -1 on error with no exception set (unless one of the indices was not None and failed to be converted to an integer, in which case -1 is returned with an exception set).
You probably do not want to use this function.
Changed in version 3.2: The parameter type for the slice parameter was PySliceObject* before.
int PySlice_GetIndicesEx(PyObject *slice, Py_ssize_t length, Py_ssize_t *start, Py_ssize_t *stop, Py_ssize_t *step, Py_ssize_t *slicelength)¶Part of the Stable ABI.
Usable replacement for PySlice_GetIndices(). Retrieve the start, stop, and step indices from the slice object slice assuming a sequence of length length, and store the length of the slice in slicelength. Out of bounds indices are clipped in a manner consistent with the handling of normal slices.
Returns 0 on success and -1 on error with exception set.
Note
This function is considered not safe for resizable sequences. Its invocation should be replaced by a combination of PySlice_Unpack() and PySlice_AdjustIndices() where
if (PySlice_GetIndicesEx(slice, length, &start, &stop, &step, &slicelength) < 0) { // return error }
is replaced by
if (PySlice_Unpack(slice, &start, &stop, &step) < 0) { // return error } slicelength = PySlice_AdjustIndices(length, &start, &stop, step);
Changed in version 3.2: The parameter type for the slice parameter was PySliceObject* before.
Changed in version 3.6.1: If Py_LIMITED_API is not set or set to the value between 0x03050400 and 0x03060000 (not including) or 0x03060100 or higher !PySlice_GetIndicesEx is implemented as a macro using !PySlice_Unpack and !PySlice_AdjustIndices. Arguments start, stop and step are evaluated more than once.
Deprecated since version 3.6.1: If Py_LIMITED_API is set to the value less than 0x03050400 or between 0x03060000 and 0x03060100 (not including) !PySlice_GetIndicesEx is a deprecated function.
int PySlice_Unpack(PyObject *slice, Py_ssize_t *start, Py_ssize_t *stop, Py_ssize_t *step)¶Part of the Stable ABI since version 3.7.
Extract the start, stop and step data members from a slice object as C integers. Silently reduce values larger than PY_SSIZE_T_MAX to PY_SSIZE_T_MAX, silently boost the start and stop values less than PY_SSIZE_T_MIN to PY_SSIZE_T_MIN, and silently boost the step values less than -PY_SSIZE_T_MAX to -PY_SSIZE_T_MAX.
Return -1 on error, 0 on success.
New in version 3.6.1.
Py_ssize_t PySlice_AdjustIndices(Py_ssize_t length, Py_ssize_t *start, Py_ssize_t *stop, Py_ssize_t step)¶Part of the Stable ABI since version 3.7.
Adjust start/end slice indices assuming a sequence of the specified length. Out of bounds indices are clipped in a manner consistent with the handling of normal slices.
Return the length of the slice. Always successful. Doesn’t call Python code.
New in version 3.6.1.
Ellipsis Object¶
PyObject *Py_Ellipsis¶The Python Ellipsis object. This object has no methods. It needs to be treated just like any other object with respect to reference counts. Like Py_None it is a singleton object.