We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
Wrong capitalization on bitgenerator MT19937
Wrong capitalization of MT19937 in default argument values of functions in numpy.random._pickle.py

### Reproducing code example:

```python
import numpy as np
np.random._pickle.__randomstate_ctor() # => error
np.random._pickle.__randomstate_ctor('mt19937') # => error
np.random._pickle.__randomstate_ctor('MT19937') # => works
```

### Error message:

*** ValueError: mt19937 is not a known BitGenerator module.

### Numpy/Python version information:

1.17.0 3.6.8 (default, Jan 14 2019, 11:02:34) 
[GCC 8.0.1 20180414 (experimental) [trunk revision 259383]]


--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `numpy/random/_pickle.py`
Content:
```
1 from .mtrand import RandomState
2 from .philox import Philox
3 from .pcg64 import PCG64
4 from .sfc64 import SFC64
5 
6 from .generator import Generator
7 from .mt19937 import MT19937
8 
9 BitGenerators = {'MT19937': MT19937,
10                  'PCG64': PCG64,
11                  'Philox': Philox,
12                  'SFC64': SFC64,
13                  }
14 
15 
16 def __generator_ctor(bit_generator_name='mt19937'):
17     """
18     Pickling helper function that returns a Generator object
19 
20     Parameters
21     ----------
22     bit_generator_name: str
23         String containing the core BitGenerator
24 
25     Returns
26     -------
27     rg: Generator
28         Generator using the named core BitGenerator
29     """
30     if bit_generator_name in BitGenerators:
31         bit_generator = BitGenerators[bit_generator_name]
32     else:
33         raise ValueError(str(bit_generator_name) + ' is not a known '
34                                                    'BitGenerator module.')
35 
36     return Generator(bit_generator())
37 
38 
39 def __bit_generator_ctor(bit_generator_name='mt19937'):
40     """
41     Pickling helper function that returns a bit generator object
42 
43     Parameters
44     ----------
45     bit_generator_name: str
46         String containing the name of the BitGenerator
47 
48     Returns
49     -------
50     bit_generator: BitGenerator
51         BitGenerator instance
52     """
53     if bit_generator_name in BitGenerators:
54         bit_generator = BitGenerators[bit_generator_name]
55     else:
56         raise ValueError(str(bit_generator_name) + ' is not a known '
57                                                    'BitGenerator module.')
58 
59     return bit_generator()
60 
61 
62 def __randomstate_ctor(bit_generator_name='mt19937'):
63     """
64     Pickling helper function that returns a legacy RandomState-like object
65 
66     Parameters
67     ----------
68     bit_generator_name: str
69         String containing the core BitGenerator
70 
71     Returns
72     -------
73     rs: RandomState
74         Legacy RandomState using the named core BitGenerator
75     """
76     if bit_generator_name in BitGenerators:
77         bit_generator = BitGenerators[bit_generator_name]
78     else:
79         raise ValueError(str(bit_generator_name) + ' is not a known '
80                                                    'BitGenerator module.')
81 
82     return RandomState(bit_generator())
83
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/numpy/random/_pickle.py b/numpy/random/_pickle.py
--- a/numpy/random/_pickle.py
+++ b/numpy/random/_pickle.py
@@ -13,7 +13,7 @@
                  }
 
 
-def __generator_ctor(bit_generator_name='mt19937'):
+def __generator_ctor(bit_generator_name='MT19937'):
     """
     Pickling helper function that returns a Generator object
 
@@ -36,7 +36,7 @@
     return Generator(bit_generator())
 
 
-def __bit_generator_ctor(bit_generator_name='mt19937'):
+def __bit_generator_ctor(bit_generator_name='MT19937'):
     """
     Pickling helper function that returns a bit generator object
 
@@ -59,7 +59,7 @@
     return bit_generator()
 
 
-def __randomstate_ctor(bit_generator_name='mt19937'):
+def __randomstate_ctor(bit_generator_name='MT19937'):
     """
     Pickling helper function that returns a legacy RandomState-like object

{"golden_diff": "diff --git a/numpy/random/_pickle.py b/numpy/random/_pickle.py\n--- a/numpy/random/_pickle.py\n+++ b/numpy/random/_pickle.py\n@@ -13,7 +13,7 @@\n                  }\n \n \n-def __generator_ctor(bit_generator_name='mt19937'):\n+def __generator_ctor(bit_generator_name='MT19937'):\n     \"\"\"\n     Pickling helper function that returns a Generator object\n \n@@ -36,7 +36,7 @@\n     return Generator(bit_generator())\n \n \n-def __bit_generator_ctor(bit_generator_name='mt19937'):\n+def __bit_generator_ctor(bit_generator_name='MT19937'):\n     \"\"\"\n     Pickling helper function that returns a bit generator object\n \n@@ -59,7 +59,7 @@\n     return bit_generator()\n \n \n-def __randomstate_ctor(bit_generator_name='mt19937'):\n+def __randomstate_ctor(bit_generator_name='MT19937'):\n     \"\"\"\n     Pickling helper function that returns a legacy RandomState-like object\n", "issue": "Wrong capitalization on bitgenerator MT19937\nWrong capitalization of MT19937 in default argument values of functions in numpy.random._pickle.py\r\n\r\n### Reproducing code example:\r\n\r\n```python\r\nimport numpy as np\r\nnp.random._pickle.__randomstate_ctor() # => error\r\nnp.random._pickle.__randomstate_ctor('mt19937') # => error\r\nnp.random._pickle.__randomstate_ctor('MT19937') # => works\r\n```\r\n\r\n### Error message:\r\n\r\n*** ValueError: mt19937 is not a known BitGenerator module.\r\n\r\n### Numpy/Python version information:\r\n\r\n1.17.0 3.6.8 (default, Jan 14 2019, 11:02:34) \r\n[GCC 8.0.1 20180414 (experimental) [trunk revision 259383]]\r\n\n", "before_files": [{"content": "from .mtrand import RandomState\nfrom .philox import Philox\nfrom .pcg64 import PCG64\nfrom .sfc64 import SFC64\n\nfrom .generator import Generator\nfrom .mt19937 import MT19937\n\nBitGenerators = {'MT19937': MT19937,\n                 'PCG64': PCG64,\n                 'Philox': Philox,\n                 'SFC64': SFC64,\n                 }\n\n\ndef __generator_ctor(bit_generator_name='mt19937'):\n    \"\"\"\n    Pickling helper function that returns a Generator object\n\n    Parameters\n    ----------\n    bit_generator_name: str\n        String containing the core BitGenerator\n\n    Returns\n    -------\n    rg: Generator\n        Generator using the named core BitGenerator\n    \"\"\"\n    if bit_generator_name in BitGenerators:\n        bit_generator = BitGenerators[bit_generator_name]\n    else:\n        raise ValueError(str(bit_generator_name) + ' is not a known '\n                                                   'BitGenerator module.')\n\n    return Generator(bit_generator())\n\n\ndef __bit_generator_ctor(bit_generator_name='mt19937'):\n    \"\"\"\n    Pickling helper function that returns a bit generator object\n\n    Parameters\n    ----------\n    bit_generator_name: str\n        String containing the name of the BitGenerator\n\n    Returns\n    -------\n    bit_generator: BitGenerator\n        BitGenerator instance\n    \"\"\"\n    if bit_generator_name in BitGenerators:\n        bit_generator = BitGenerators[bit_generator_name]\n    else:\n        raise ValueError(str(bit_generator_name) + ' is not a known '\n                                                   'BitGenerator module.')\n\n    return bit_generator()\n\n\ndef __randomstate_ctor(bit_generator_name='mt19937'):\n    \"\"\"\n    Pickling helper function that returns a legacy RandomState-like object\n\n    Parameters\n    ----------\n    bit_generator_name: str\n        String containing the core BitGenerator\n\n    Returns\n    -------\n    rs: RandomState\n        Legacy RandomState using the named core BitGenerator\n    \"\"\"\n    if bit_generator_name in BitGenerators:\n        bit_generator = BitGenerators[bit_generator_name]\n    else:\n        raise ValueError(str(bit_generator_name) + ' is not a known '\n                                                   'BitGenerator module.')\n\n    return RandomState(bit_generator())\n", "path": "numpy/random/_pickle.py"}], "after_files": [{"content": "from .mtrand import RandomState\nfrom .philox import Philox\nfrom .pcg64 import PCG64\nfrom .sfc64 import SFC64\n\nfrom .generator import Generator\nfrom .mt19937 import MT19937\n\nBitGenerators = {'MT19937': MT19937,\n                 'PCG64': PCG64,\n                 'Philox': Philox,\n                 'SFC64': SFC64,\n                 }\n\n\ndef __generator_ctor(bit_generator_name='MT19937'):\n    \"\"\"\n    Pickling helper function that returns a Generator object\n\n    Parameters\n    ----------\n    bit_generator_name: str\n        String containing the core BitGenerator\n\n    Returns\n    -------\n    rg: Generator\n        Generator using the named core BitGenerator\n    \"\"\"\n    if bit_generator_name in BitGenerators:\n        bit_generator = BitGenerators[bit_generator_name]\n    else:\n        raise ValueError(str(bit_generator_name) + ' is not a known '\n                                                   'BitGenerator module.')\n\n    return Generator(bit_generator())\n\n\ndef __bit_generator_ctor(bit_generator_name='MT19937'):\n    \"\"\"\n    Pickling helper function that returns a bit generator object\n\n    Parameters\n    ----------\n    bit_generator_name: str\n        String containing the name of the BitGenerator\n\n    Returns\n    -------\n    bit_generator: BitGenerator\n        BitGenerator instance\n    \"\"\"\n    if bit_generator_name in BitGenerators:\n        bit_generator = BitGenerators[bit_generator_name]\n    else:\n        raise ValueError(str(bit_generator_name) + ' is not a known '\n                                                   'BitGenerator module.')\n\n    return bit_generator()\n\n\ndef __randomstate_ctor(bit_generator_name='MT19937'):\n    \"\"\"\n    Pickling helper function that returns a legacy RandomState-like object\n\n    Parameters\n    ----------\n    bit_generator_name: str\n        String containing the core BitGenerator\n\n    Returns\n    -------\n    rs: RandomState\n        Legacy RandomState using the named core BitGenerator\n    \"\"\"\n    if bit_generator_name in BitGenerators:\n        bit_generator = BitGenerators[bit_generator_name]\n    else:\n        raise ValueError(str(bit_generator_name) + ' is not a known '\n                                                   'BitGenerator module.')\n\n    return RandomState(bit_generator())\n", "path": "numpy/random/_pickle.py"}]}