ECDSA Signing and verifying signatures between Python and JS I create a signature on js, here jsrsasign
Signatures are obtained in the format:

3045022045c61e649ca9f6011a8d34ac865c4780421de08ff50ac3dad0da36043b6de478022100b19208d1ec51f6dd6f6b725342618f55f9fc90c96c5b5409998d66774749a0b


Always start with 30 ...
In Python, I use the python-ecdsa library. 
In this library, the signature format is

a8c7dd7e9b669b1bc841ddf66bc08b10bc1112fa14fce2a5a2246edf997c577450af6b9edfe373546e17ab7363c097ab468db04ed707fb65992e20eabfd1bf40


Therefore, verification does not occur.
How to bring signatures to one format?
An ECDSA signature is, formally, a pair of integers $(r,s)$. There are two main conventions for encoding these integers into bytes:


Encode both integers into unsigned big-endian, using the same size for both, and concatenate the values. This is the traditional way in, for instance, PKCS#11 and OpenPGP; python-ecdsa apparently uses that format.
Encode the integers as an ASN.1/DER structure (a SEQUENCE of two INTEGER values). This is what is normally used in everything that relates to X.509 certificates, and also in SSL/TLS exchanges. jsrsasign apparently uses that format.


Conversion between these formats can be done, but it is surprisingly tricky to do correctly (it's a parser, after all). It seems that python-ecdsa can also encode and decode ASN.1-based signatures (see the functions sigencode_der() and sigdecode_der(), for instance).