CLN: unify numpy.random-related imports
- [x] closes #37053 ~~(keep this issue open until both #37492 and #37117 are completed)~~
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

# update 2020-10-30
This is the replacement for #37103, since I messed up the git timeline in the previous PR(the conflicts are too complex to fix). The separate CI is in #37117.

The whole project is reformatted except `pandas/_testing.py` for there are quite a few `tm.randn` used in testing files.

below is the script to do the whole clean-up
```
import os
import re


class NumpyRandomRelatedScript:
    def __init__(self, base_dir: str = "/dir/of/pandas/pandas") -> None:
        self.base_dir = base_dir
        self.py_files = []
        self.backup_files = []
        self.p1 = re.compile("import numpy as np")
        self.p2 = re.compile("from numpy.random import[ ,a-zA-Z]*[\s]")
        self.p3 = re.compile("from numpy import random[\s]")

    def search_py_files(self, pandas_file_dir: str) -> None:
        if os.path.isfile(pandas_file_dir):
            if pandas_file_dir[-3:] == ".py":
                if pandas_file_dir != os.path.join(self.base_dir, "_testing.py"):
                    self.py_files.append(pandas_file_dir)
        elif os.path.isdir(pandas_file_dir):
            for d in os.listdir(pandas_file_dir):
                self.search_py_files(os.path.join(pandas_file_dir, d))

    def do_the_clean_up(self, file_dir: str) -> None:
        with open(file_dir, "r") as file:
            data = file.read()
            m1, m2, m3 = (
                re.search(self.p1, data),
                re.search(self.p2, data),
                re.search(self.p3, data),
            )
            if not (m2 or m3):
                # print("There's no need to change, please recheck!")
                return

        backup_dir = file_dir + ".issue37053_backup"
        self.backup_files.append(backup_dir)
        print("Backup: " + backup_dir)
        with open(backup_dir, "w+") as file:
            file.write(data)

        with open(file_dir, "w+") as file:
            if m2:
                if not m1:
                    data = re.sub(self.p2, "import numpy as np\n", data)
                    m1 = True
                else:
                    data = re.sub(self.p2, "", data)
                methods = (
                    m2.group(0)
                    .replace("from numpy.random import", "")
                    .replace(" ", "")
                    .replace("\n", "")
                    .split(",")
                )
                if isinstance(methods, str):
                    methods = [methods]
                for method in methods:
                    data = re.sub(
                        r"[\s]{meth}[^a-z]".format(meth=method),
                        " np.random.{meth}(".format(meth=method),
                        data,
                    )
                    data = re.sub(
                        r"[\s]-{meth}[^a-z]".format(meth=method),
                        " -np.random.{meth}(".format(meth=method),
                        data,
                    )
                    data = re.sub(
                        r"[\(]{meth}[^a-z]".format(meth=method),
                        "(np.random.{meth}(".format(meth=method),
                        data,
                    )
            if m3:
                if not m1:
                    data = re.sub(self.p3, "import numpy as np\n", data)
                else:
                    data = re.sub(self.p3, "", data)
                data = re.sub(r"[\s]random.{1}", " np.random.", data)
                data = re.sub(r"[\(]random.{1}", "(np.random.", data)
            file.write(data)
            print("Clean: " + file_dir)

    def remove_backup(self) -> None:
        for file in self.backup_files:
            print("Remove: " + file)
            os.remove(file)


if __name__ == "__main__":
    script = NumpyRandomRelatedScript()
    script.search_py_files(script.base_dir)
    for f in script.py_files:
        script.do_the_clean_up(f)
    script.remove_backup()
```
> Thanks @onshek!
> 
> Here or in a follow-on we'd like to add a CI check to enforce this in future PRs (unless it's already here and I missed it)

Hi @arw2019 , the separate CI is in #37117.  I wonder are these errors caused by my change? > Hi @arw2019 , the separate CI is in #37117. I wonder are these errors caused by my change?

The CI failures? I don't think so. Some lines can be a bit flaky I see, thanks @arw2019 !
@jreback @charlesdong1991 @jbrockmendel let me know if where's any problem, thanks! thanks @onshek happy to have a follow for the check (which you can implement using the pre-commit); we already do somethings like this, e.g. to enforce imports of DataFrame,Series and so on (so similar but a slightly different check) > thanks @onshek happy to have a follow for the check (which you can implement using the pre-commit); we already do somethings like this, e.g. to enforce imports of DataFrame,Series and so on (so similar but a slightly different check)

Is this ? commit https://github.com/pandas-dev/pandas/blob/master/.pre-commit-config.yaml
Then do I need to convert the related check in #37117  into the pre-commit file?