See the manpage [here](https://man7.org/linux/man-pages/man2/recv.2.html) for C.
See [here](https://docs.python.org/3/library/socket.html#:~:text=socket.recv) for Python.
The `recv()` call is (normally) only used on a connected socket.

## C
From the manpage
```c
#include <sys/socket.h>

ssize_t recv(int sockfd, void *buf, size_t len, int flags);
ssize_t recvfrom(int sockfd, void *restrict buf, size_t len, int flags,
                 struct sockaddr *restrict src_addr,
                 socklen_t *restrict addrlen);
ssize_t recvmsg(int sockfd, struct msghdr *msg, int flags);
```
The **return value** is:
* the number of bytes received, if positive;
* zero for when a socket has performed an orderly shutdown
* -1 on error.

## Python
Basically the same as C, except
```python
import socket
s = socket.socket(...)
number_of_bytes = s.recv(size_of_buffer)
```