About the solution to prompt modulenotfounderror: no module named'pymongo 'when running the scratch project

1 Problem description

Use today scrapy The framework writes crawlers and uses mongodb When storing results , stay powershell Run in scrapy crawl demo Found an error , What is the content of the error report No module named 'pymongo‘, namely , Can't find pymongo modular , But I have actually downloaded this module , So what's going on ？

2 Problem analysis

First , It's important to point out that , It must be an environmental problem . Is it multiple python Version co-existence ？ In my computer, there are Python2.7 and python3.6, At the beginning, it was installation anaconda when , The former is installed by default , The latter is required for work and study , meanwhile Python2 Will be eliminated , Installed Python3, As a result, there are two environments in my computer at the same time , and , The author will pymongo Installed in python36 in , Not installed in Python27 in , Lead to in powershell Run in scrapy By default python2.7, Therefore, the above error report is caused , So is it ？

3 Test the hypothesis

The best way to test a hypothesis is to try , Here the author first posts powershell Mistakes in ：

Here, try the default Python27 You can also download this in the environment pymongo modular , Run it again , See if there is an error , give the result as follows ：
It is found that it can run correctly , It seems that this is the problem , That is, it runs directly at the terminal scrapy The program will default to conda Of Python The default path , I am here Python2.7.

4 other

Use here cmd Try the terminal method , because powershell Count as cmd Upgraded version , The author has been tested （ To uninstall first Python2.7 Of pymongo Install again ） Separate tests found , It's really this conda Problems caused by the default environment of , But in the course of my test , And found a powershell problem , That is, it cannot be like cmd Switching environment ： The following are in cmd and powershell Switch in Python Environment debugging

conda activate python Version number 
 I am here 36, Because it was installed conda When the default 27
conda activate Python36

Discover successful switching environments , But in powershell You can't

therefore , Here we need to pay attention to , But since in cmd Environment can be switched in , Well, because I started with scrapy Is in python36 Written in , The reason for the mistake is powershell Only recognize the default Python27 edition , And I am Python27 There is no installation in pymongo, stay Python36 This module is installed in , So I am cmd Switch to Python36 Then run scrapy Just file it ？
True knowledge comes from practice ：
It works

5 summary

Many people need to work and study , There will be multiple in the computer at the same time Python edition ,
（1） stay powershell function scrapy File program , Will be used by default conda Default environment , If there is no corresponding third-party module installed in the default environment , A similar error occurs when the module cannot be found , So you can install the same module in the default environment , At the same time, continue to use powershell start-up ;
（2） As the author found in the above analysis ,powershell Unable to switch environment , If you don't have to use powershell, It can be found at the terminal cmd in , Switch Python After interpreter , because pymongo Installed in the Python36 It's in , After switching, you can run directly .
All in all , If there is no multi version coexistence problem , There will be no problem with this article ; At the same time, if powershell It will also save a lot if you can switch versions debug Time .