pip3: command not found

I want to install TensorFlow following these instructions: https://web.archive.org/web/20170627102751/https://www.tensorflow.org/versions/r0.12/get_started/os_setup#pip_installation

But when I try this code on terminal, it returns an error.

$ sudo pip3 install --upgrade $TF_BINARY_URL
sudo: pip3: command not found

So I installed Homebrew and tried to uninstall and reinstall python3-pip, but didn't work.

MakotonoMacBook-ea:~ makotomiyazaki$ brew uninstall python3-pip
Error: No such keg: /usr/local/Cellar/python3-pip

MakotonoMacBook-ea:~ makotomiyazaki$ brew install python3-pip
Error: No available formula with the name "python3-pip" 
==> Searching for a previously deleted formula...
Warning: homebrew/core is shallow clone. To get complete history run:
  git -C "$(brew --repo homebrew/core)" fetch --unshallow

What should I do for getting pip3?
My OS is macOS High Sierra, and I have Python 3.6.2 already installed.

EDIT: I tried

python3 -m pip

and what's returned was this:

The directory '/Users/makotomiyazaki/Library/Caches/pip/http' or its 
parent directory is not owned by the current user and the cache has 
been disabled. Please check the permissions and owner of that 
directory. If executing pip with sudo, you may want sudo's -H flag.
The directory '/Users/makotomiyazaki/Library/Caches/pip' or its parent 
directory is not owned by the current user and caching wheels has been 
disabled. check the permissions and owner of that directory. If 
executing pip with sudo, you may want sudo's -H flag.
You must give at least one requirement to install (see "pip help 
install")

I also tried which pip3, but just I don't know if it worked...

MakotonoMacBook-ea:~ makotomiyazaki$ sudo which pip3 install --upgrade $TF_BINARY_URL
/usr/bin/install

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