Question

For example, I want to check a string and if it is not convertible to integer(with int()), how can I detect that?

Answer 1

Use the .isdigit() method:

>>> '123'.isdigit()
True
>>> '1a23'.isdigit()
False

Quoting the documentation:

Return true if all characters in the string are digits and there is at least one character, false otherwise.

For unicode strings or Python 3 strings, you’ll need to use a more precise definition and use the unicode.isdecimal() / str.isdecimal() instead; not all Unicode digits are interpretable as decimal numbers. U+00B2 SUPERSCRIPT 2 is a digit, but not a decimal, for example.