Return substrings from Tensor of strings.


  • tf.compat.v1.substr
  • tf.substr

Defined in python/ops/

For each string in the input Tensor, creates a substring starting at index pos with a total length of len.

If len defines a substring that would extend beyond the length of the input string, then as many characters as possible are used.

A negative pos indicates distance within the string backwards from the end.

If pos specifies an index which is out of range for any of the input strings, then an InvalidArgumentError is thrown.

pos and len must have the same shape, otherwise a ValueError is thrown on Op creation.

NOTE: Substr supports broadcasting up to two dimensions. More about broadcasting here


Using scalar pos and len:

input = [b'Hello', b'World']
position = 1
length = 3

output = [b'ell', b'orl']

Using pos and len with same shape as input:

input = [[b'ten', b'eleven', b'twelve'],
         [b'thirteen', b'fourteen', b'fifteen'],
         [b'sixteen', b'seventeen', b'eighteen']]
position = [[1, 2, 3],
            [1, 2, 3],
            [1, 2, 3]]
length =   [[2, 3, 4],
            [4, 3, 2],
            [5, 5, 5]]

output = [[b'en', b'eve', b'lve'],
          [b'hirt', b'urt', b'te'],
          [b'ixtee', b'vente', b'hteen']]

Broadcasting pos and len onto input:

input = [[b'ten', b'eleven', b'twelve'],
         [b'thirteen', b'fourteen', b'fifteen'],
         [b'sixteen', b'seventeen', b'eighteen'],
         [b'nineteen', b'twenty', b'twentyone']]
position = [1, 2, 3]
length =   [1, 2, 3]

output = [[b'e', b'ev', b'lve'],
          [b'h', b'ur', b'tee'],
          [b'i', b've', b'hte'],
          [b'i', b'en', b'nty']]

Broadcasting input onto pos and len:

input = b'thirteen'
position = [1, 5, 7]
length =   [3, 2, 1]

output = [b'hir', b'ee', b'n']


  • input: A Tensor of type string. Tensor of strings
  • pos: A Tensor. Must be one of the following types: int32, int64. Scalar defining the position of first character in each substring
  • len: A Tensor. Must have the same type as pos. Scalar defining the number of characters to include in each substring
  • unit: An optional string from: "BYTE", "UTF8_CHAR". Defaults to "BYTE". The unit that is used to create the substring. One of: "BYTE" (for defining position and length by bytes) or "UTF8_CHAR" (for the UTF-8 encoded Unicode code points). The default is "BYTE". Results are undefined if unit=UTF8_CHAR and the input strings do not contain structurally valid UTF-8.
  • name: A name for the operation (optional).


A Tensor of type string.