What is a multiprocessing.Value and Array?

Question

Accepted Answer

**Value** and **Array** provide **shared memory** objects for simple data types.

```python
from multiprocessing import Process, Value, Array

def increment(counter):
    for _ in range(1000):
        with counter.get_lock():
            counter.value += 1

if __name__ == "__main__":
    # Shared integer
    counter = Value("i", 0)  # "i" = signed int

processes = [
        Process(target=increment, args=(counter,))
        for _ in range(4)
    ]

for p in processes:
        p.start()
    for p in processes:
        p.join()

print(counter.value)  # 4000

# Shared array
    arr = Array("d", [1.0, 2.0, 3.0, 4.0])  # "d" = double
    print(arr[:])  # [1.0, 2.0, 3.0, 4.0]
```

**Type codes:**
- "i" — signed int.
- "d" — double.
- "c" — char.
- "f" — float.

**Methods:**
- `get_lock()` — synchronization.
- `get_obj()` — get raw ctypes object.
- `.value` — get/set value.

Python: What is a multiprocessing.Value and Array?