试图通过pip
在python2中可以很方便的安装progressbar模块，但是python3中会报如下错误：
```python
Collecting progressbar
Downloading progressbar-2.3.tar.gz
Complete output from command python setup.py egg_info:
Traceback (most recent call last):
File "", line 1, in
File "/tmp/pip-build-ghlr5eic/progressbar/setup.py", line 5, in
import progressbar
File "/tmp/pip-build-ghlr5eic/progressbar/progressbar/init.py", line 59, in
from progressbar.widgets import *
File "/tmp/pip-build-ghlr5eic/progressbar/progressbar/widgets.py", line 121, in
class FileTransferSpeed(Widget):
File "/home/wenfeng/anaconda3/envs/tensorflow/lib/python3.6/abc.py", line 133, in new
cls = super().new(mcls, name, bases, namespace, **kwargs)
ValueError: 'format' in slots conflicts with class variable