TechOverflow

Jan

2022

How much current can Molex Mini-Fit Jr contacts take (ampacity)?

Molex Mini-Fit Jr contacts like the 39000082 typically have an ampacity of 9.0A per contact. Source: Molex 39000082 datasheet.

Jan

2022

M12 connector: How much current / ampacity per contact?

Typical M12 connectors have an ampacity of around 4A per contact. For example, see the Phoenix SACC-M12FR-5PL 5-pin M12 connector

Jan

2022

Angular: ActivatedRoute minimal example

For this route:

{path: 'my/:id', component: MyDashboardComponent},

this is how you can use it in MyDashboardComponent:

constructor(private route: ActivatedRoute) {
      this.route.params.subscribe(params => {
          console.info(params.id);
      })
}

Jan

2022

How to split strings in C++ using boost::algorithm::split() – a minimal example

#include <boost/algorithm/string/split.hpp> // boost::algorithm::split
#include <boost/algorithm/string/classification.hpp> // boost::is_any_of
#include <string>
#include <iostream>
#include <vector>

int main() {
    std::string mystr = "foo-bar-x";
    // Split by "-"
    std::vector<std::string> splitResult;
    boost::algorithm::split(splitResult, mystr, boost::is_any_of("-"));
    // Print results, one line at a time
    // Prints:
    // foo
    // bar
    // x
    for(const std::string& s : splitResult) {
        std::cout << s << std::endl;
    }
}

Jan

2022

How to link the boost string algorithms library – which linker flags to use?

You do not need to link the boost::algorithm library. It is a header only library, hence you only need to #include its header files.

For examples, see

Jan

2022

How to use boost string algorithm starts_with: A minimal example

#include <boost/algorithm/string/predicate.hpp>
#include <string>
#include <iostream>

int main() {
    std::string mystr = "foobar";
    // Prints "true, false"
    std::cout << std::boolalpha
        << boost::algorithm::starts_with(mystr, "foo") << ", "
        << boost::algorithm::starts_with(mystr, "bar") << std::endl;
}

Also see: How to use boost string algorithm ends_with: A minimal example

Jan

2022

How to use boost string algorithm ends_with: A minimal example

#include <boost/algorithm/string/predicate.hpp>
#include <string>
#include <iostream>

int main() {
    std::string mystr = "foobar";
    // Prints "false, true"
    std::cout << std::boolalpha
        << boost::algorithm::ends_with(mystr, "foo") << ", "
        << boost::algorithm::ends_with(mystr, "bar") << std::endl;
}

Also see: How to use boost string algorithm starts_with: A minimal example

Jan

2022

What does sdist mean in Python?

sdist means source distribution. It is an archive (usually a .tar.gz) that contains all the source files and related data for a project in a single archive. A source distribution is what is downloaded from the PyPI package registry when you run pip install.

You can create the source distribution (sdist) for a project using

python setup.py sdist

Jan

2022

How to fix MANIFEST.in graft having no effect on Windows

Problem:

In your MANIFEST.in, you have a line like

graft src/

but when you run

python setup.py sdist

some file in src is not included in the archive

Solution:

This is due to the slash at the end of src/! The slash works fine on Linux, but on Windows, backslashes are used to separate directory names. You can just remove the slash after src, it doesn’t serve any purpose on Windows or Linux:

graft src

After that, retry and you should see your file being included in the sdist archive.

Jan

2022

How to fix Python CFFI package not finding include file when running pip install

Problem:

When you install your package locally using python setup.py install, all include files are found and the package installs correctly

However you run pip install, the compiler is missing some include files

Solution:

Most likely, your include file does not end up in the sdist i.e. the source distribution .tar.gz file. In order to include it, create a MANIFEST.in file in the same folder as setup.py in order to tell setuptools what to include in addition to any file directly referenced in setup.py.

In my case, the include files are in the src folder so I add this to MANIFEST.in:

graft src/

Now, to check if that worked, run

python setup.py sdist

which will show you which files are included in the source distribution. Example:

C:\Users\ukoeh\cv_algorithms>python setup.py sdist
running sdist
running egg_info
writing cv_algorithms.egg-info\PKG-INFO
writing dependency_links to cv_algorithms.egg-info\dependency_links.txt
writing requirements to cv_algorithms.egg-info\requires.txt
writing top-level names to cv_algorithms.egg-info\top_level.txt
reading manifest file 'cv_algorithms.egg-info\SOURCES.txt'
reading manifest template 'MANIFEST.in'
adding license file 'LICENSE'
writing manifest file 'cv_algorithms.egg-info\SOURCES.txt'
running check
warning: check: missing meta-data: either (author and author_email) or (maintainer and maintainer_email) should be supplied

creating cv_algorithms-1.0.4
creating cv_algorithms-1.0.4\cv_algorithms
creating cv_algorithms-1.0.4\cv_algorithms.egg-info
creating cv_algorithms-1.0.4\src
creating cv_algorithms-1.0.4\test
copying files to cv_algorithms-1.0.4...
copying LICENSE -> cv_algorithms-1.0.4
copying MANIFEST.in -> cv_algorithms-1.0.4
copying README.md -> cv_algorithms-1.0.4
copying setup.py -> cv_algorithms-1.0.4
copying cv_algorithms\__init__.py -> cv_algorithms-1.0.4\cv_algorithms
copying cv_algorithms\_checks.py -> cv_algorithms-1.0.4\cv_algorithms
copying cv_algorithms\_ffi.py -> cv_algorithms-1.0.4\cv_algorithms
copying cv_algorithms\classification.py -> cv_algorithms-1.0.4\cv_algorithms
copying cv_algorithms\colorspace.py -> cv_algorithms-1.0.4\cv_algorithms
copying cv_algorithms\contours.py -> cv_algorithms-1.0.4\cv_algorithms
copying cv_algorithms\distance.py -> cv_algorithms-1.0.4\cv_algorithms
copying cv_algorithms\grassfire.py -> cv_algorithms-1.0.4\cv_algorithms
copying cv_algorithms\morphology.py -> cv_algorithms-1.0.4\cv_algorithms
copying cv_algorithms\neighbours.py -> cv_algorithms-1.0.4\cv_algorithms
copying cv_algorithms\popcount.py -> cv_algorithms-1.0.4\cv_algorithms
copying cv_algorithms\text.py -> cv_algorithms-1.0.4\cv_algorithms
copying cv_algorithms\thinning.py -> cv_algorithms-1.0.4\cv_algorithms
copying cv_algorithms\utils.py -> cv_algorithms-1.0.4\cv_algorithms
copying cv_algorithms.egg-info\PKG-INFO -> cv_algorithms-1.0.4\cv_algorithms.egg-info
copying cv_algorithms.egg-info\SOURCES.txt -> cv_algorithms-1.0.4\cv_algorithms.egg-info
copying cv_algorithms.egg-info\dependency_links.txt -> cv_algorithms-1.0.4\cv_algorithms.egg-info
copying cv_algorithms.egg-info\not-zip-safe -> cv_algorithms-1.0.4\cv_algorithms.egg-info
copying cv_algorithms.egg-info\requires.txt -> cv_algorithms-1.0.4\cv_algorithms.egg-info
copying cv_algorithms.egg-info\top_level.txt -> cv_algorithms-1.0.4\cv_algorithms.egg-info
copying src\common.hpp -> cv_algorithms-1.0.4\src
copying src\distance.cpp -> cv_algorithms-1.0.4\src
copying src\grassfire.cpp -> cv_algorithms-1.0.4\src
copying src\neighbours.cpp -> cv_algorithms-1.0.4\src
copying src\popcount.cpp -> cv_algorithms-1.0.4\src
copying src\thinning.cpp -> cv_algorithms-1.0.4\src
copying src\windows.cpp -> cv_algorithms-1.0.4\src
copying test\TestColorspace.py -> cv_algorithms-1.0.4\test
copying test\TestContours.py -> cv_algorithms-1.0.4\test
copying test\TestDistance.py -> cv_algorithms-1.0.4\test
copying test\TestGrassfire.py -> cv_algorithms-1.0.4\test
copying test\TestNeighbours.py -> cv_algorithms-1.0.4\test
copying test\TestPopcount.py -> cv_algorithms-1.0.4\test
copying test\TestThinning.py -> cv_algorithms-1.0.4\test
copying test\TestUtils.py -> cv_algorithms-1.0.4\test
copying test\__init__.py -> cv_algorithms-1.0.4\test
Writing cv_algorithms-1.0.4\setup.cfg
Creating tar archive
removing 'cv_algorithms-1.0.4' (and everything under i

After that, you need to re-release your package. See my cv_algorithms project for a complete example.

Jan

2022

How to fix Python ModuleNotFoundError: No module named ‘cv2’ on Windows

Problem:

You see an error message like the following one when running some Python code on Windows:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\ukoeh\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.9_qbz5n2kfra8p0\LocalCache\local-packages\Python39\site-packages\cv_algorithms\__init__.py", line 5, in <module>
    from .text import *
  File "C:\Users\ukoeh\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.9_qbz5n2kfra8p0\LocalCache\local-packages\Python39\site-packages\cv_algorithms\text.py", line 7, in <module>
    import cv2
ModuleNotFoundError: No module named 'cv2'

Solution:

Install the opencv-python package using

pip install opencv-python

and retry.

Jan

2022

How to fix Python CFFI error LNK2001: unresolved external symbol PyInit__…

Problem:

When trying to install your Python library using a C module on Windows, you see an error message like

LINK : error LNK2001: unresolved external symbol PyInit__cv_algorithms
build\temp.win-amd64-3.6\Release\src_cv_algorithms.cp36-win_amd64.lib : fatal error LNK1120: 1 unresolved externals
error: command 'C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\BIN\x86_amd64\link.exe' failed with exit status 1120

Solution:

On Windows, CFFI does not properly generate the.

You can easily fix that by adding a template function and including that only on windows: I suggest creating windows.cpp like this:

/**
 * This contains hacks to get the installation on Windows working.
 * This fixes error LNK2001: unresolved external symbol PyInit__cv_algorithms
 */
void PyInit__cv_algorithms(void) { }

Copy & paste the name of the function from the error message! The fix will not work if you use the wrong function name.

Example how to include that file only on Windows:

platform_src = ["src/windows.cpp"] if os.name == 'nt' else []

mod_cv_algorithms = Extension('cv_algorithms._cv_algorithms',
                         sources=['src/main.cpp'] + platform_src)

For a full example, see cv_algorithms where I first implemented this fix.

Jan

2022

How to fix ufw [UFW BLOCK] message spamming syslog / dmesg

Problem:

In your syslog which you can see using

dmesg

you see a lot of [UFW BLOCK] messages like these:

[600810.355752] [UFW BLOCK] IN=enp0s3 OUT= MAC=02:00:17:02:76:ad:00:00:17:b9:55:d6:08:00 SRC=45.146.164.226 DST=10.0.0.130 LEN=40 TOS=0x00 PREC=0x00 TTL=251 ID=59316 PROTO=TCP SPT=48741 DPT=50713 WINDOW=1024 RES=0x00 SYN URGP=0 
[600831.477953] [UFW BLOCK] IN=enp0s3 OUT= MAC=02:00:17:02:76:ad:00:00:17:b9:55:d6:08:00 SRC=74.118.36.15 DST=10.0.0.130 LEN=40 TOS=0x00 PREC=0x00 TTL=58 ID=59050 PROTO=TCP SPT=7527 DPT=23 WINDOW=14663 RES=0x00 SYN URGP=0 
[600853.366152] [UFW BLOCK] IN=enp0s3 OUT= MAC=02:00:17:02:76:ad:00:00:17:b9:55:d6:08:00 SRC=34.77.162.17 DST=10.0.0.130 LEN=44 TOS=0x00 PREC=0x00 TTL=253 ID=51373 PROTO=TCP SPT=50218 DPT=5900 WINDOW=1024 RES=0x00 SYN URGP=0 
[600876.538979] [UFW BLOCK] IN=enp0s3 OUT= MAC=02:00:17:02:76:ad:00:00:17:b9:55:d6:08:00 SRC=74.118.36.15 DST=10.0.0.130 LEN=40 TOS=0x00 PREC=0x00 TTL=58 ID=59050 PROTO=TCP SPT=7527 DPT=23 WINDOW=14663 RES=0x00 SYN URGP=0

Solution:

Disable ufw logging using

sudo ufw logging off

and no new messages should appear.

Jan

2022

Paramiko SSH client minimal example: How to connect to SSH server and execute command

This example shows how to use paramiko to connect to [email protected] using the SSH key stored in ~/.ssh/id_ed25519, execute the command ls and print its output. Since paramiko is a pure Python implementation of SSH, this does not require SSH clients to be installed.

import os.path
import paramiko

ssh = paramiko.SSHClient()
ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
ssh.connect("192.168.1.112", username="user",
            key_filename=os.path.join(os.path.expanduser('~'), ".ssh", "id_ed25519"))

# Example command:
stdin, stdout, stderr = ssh.exec_command("ls")
output = stdout.read()
print(output)

# Cleanup
ssh.close()

Jan

2022

Paramiko: How to execute command and get output as string

Using exec_command() in Paramiko returns a tuple (stdin, stdout, stderr). Most of the time, you just want to read stdout and ignore stdin and stderr. You can get the output the command by using stdout.read()(returns a string) or stdout.readlines() (returns a list of lines).

Example:

stdin, stdout, stderr = ssh.exec_command("ls")
output = stdout.read()
print(output)

Also see our full example: Paramiko SSH client minimal example: How to connect to SSH server and execute command

Jan

2022

Paramiko SSH client: How to connect using public key authentication

This example shows how to use paramiko to connect to [email protected] using the SSH key stored in ~/.ssh/id_ed25519 using Python:

import os.path
import paramiko

ssh = paramiko.SSHClient()
ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
ssh.connect("192.168.1.112", username="user",
            key_filename=os.path.join(os.path.expanduser('~'), ".ssh", "id_ed25519"))

Also see our full example: Paramiko SSH client minimal example: How to connect to SSH server and execute command

Jan

2022

How to fix Paramiko SSHException: Server … not found in known_hosts

Problem:

When trying to connect to a SSH server using paramiko using code like

ssh = paramiko.SSHClient()
ssh.connect("192.168.1.112")

you see an error message like

SSHException: Server '192.168.1.112' not found in known_hosts

Solution:

The simplest solution is to add

ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())

before the call to connect():

ssh = paramiko.SSHClient()
ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
ssh.connect("192.168.1.112")

This will automatically add unknown host keys to the known hosts store. Note that this to some extent defeats the purpose of verifying host keys and you should manually verify host keys if possible. However, in many applications, there is no-one there to verify host keys in an automated process and thus this solution is more practical. Just keep in mind its security implications.

Jan

2022

How to fix conan install ERROR: Missing binary

Problem:

When running

conan install .

you see ERROR: Missing binary error messages like this:

Installing (downloading, building) binaries...
ERROR: Missing binary: cpr/1.6.2:76fe60a9d5c829a2384b0f578695b5a6357b8acc
ERROR: Missing binary: gtest/cci.20210126:c37dc23725d84483088a68c29e2dd7122c328359
ERROR: Missing binary: jsoncpp/1.9.4:718278bac9f92b77a9a44bfbe1aa00d1c8344d51
ERROR: Missing binary: libcurl/7.78.0:d287dc966931230205222ceabf47400733e72fa3
ERROR: Missing binary: openssl/1.1.1l:c3baf9fae083edda2e0c5ef3337b6a111016a898
ERROR: Missing binary: zlib/1.2.11:c3baf9fae083edda2e0c5ef3337b6a111016a898

Solution:

Use the --build flag for conan install to enable building the dependencies for which no binaries are available:

conan install . --build

Complete error log example

Configuration:
[settings]
arch=armv8
arch_build=armv8
build_type=Release
compiler=gcc
compiler.libcxx=libstdc++
compiler.version=9
os=Linux
os_build=Linux
[options]
[build_requires]
[env]

openssl/1.1.1l: Not found in local cache, looking in remotes...
openssl/1.1.1l: Trying with 'conancenter'...
Downloading conanmanifest.txt completed [0.26k]                                          
Downloading conanfile.py completed [40.47k]                                              
Downloading conan_export.tgz completed [0.25k]                                           
Decompressing conan_export.tgz completed [0.00k]                                         
openssl/1.1.1l: Downloaded recipe revision 0
cpr/1.6.2: Not found in local cache, looking in remotes...
cpr/1.6.2: Trying with 'conancenter'...
Downloading conanmanifest.txt completed [0.25k]                                          
Downloading conanfile.py completed [9.62k]                                               
Downloading conan_export.tgz completed [0.30k]                                           
Decompressing conan_export.tgz completed [0.00k]                                         
cpr/1.6.2: Downloaded recipe revision 0
WARN: cpr/1.6.2: requirement libcurl/7.80.0 overridden by elasticlient/0.2 to libcurl/7.78.0 
libcurl/7.78.0: Not found in local cache, looking in remotes...
libcurl/7.78.0: Trying with 'conancenter'...
Downloading conanmanifest.txt completed [0.70k]                                          
Downloading conanfile.py completed [27.11k]                                              
Downloading conan_export.tgz completed [0.23k]                                           
Decompressing conan_export.tgz completed [0.00k]                                         
libcurl/7.78.0: Downloaded recipe revision 0
jsoncpp/1.9.4: Not found in local cache, looking in remotes...
jsoncpp/1.9.4: Trying with 'conancenter'...
Downloading conanmanifest.txt completed [0.65k]                                          
Downloading conanfile.py completed [4.90k]                                               
Downloading conan_export.tgz completed [0.25k]                                           
Decompressing conan_export.tgz completed [0.00k]                                         
jsoncpp/1.9.4: Downloaded recipe revision 0
gtest/cci.20210126: Not found in local cache, looking in remotes...
gtest/cci.20210126: Trying with 'conancenter'...
Downloading conanmanifest.txt completed [0.39k]                                          
Downloading conanfile.py completed [8.14k]                                               
Downloading conan_export.tgz completed [0.32k]                                           
Decompressing conan_export.tgz completed [0.00k]                                         
gtest/cci.20210126: Downloaded recipe revision 0
conanfile.py (elasticlient/0.2): Installing package
Requirements
    cpr/1.6.2 from 'conancenter' - Downloaded
    jsoncpp/1.9.4 from 'conancenter' - Downloaded
    libcurl/7.78.0 from 'conancenter' - Downloaded
    openssl/1.1.1l from 'conancenter' - Downloaded
    zlib/1.2.11 from 'conancenter' - Cache
Packages
    cpr/1.6.2:76fe60a9d5c829a2384b0f578695b5a6357b8acc - Missing
    jsoncpp/1.9.4:718278bac9f92b77a9a44bfbe1aa00d1c8344d51 - Missing
    libcurl/7.78.0:d287dc966931230205222ceabf47400733e72fa3 - Missing
    openssl/1.1.1l:c3baf9fae083edda2e0c5ef3337b6a111016a898 - Missing
    zlib/1.2.11:c3baf9fae083edda2e0c5ef3337b6a111016a898 - Missing
Build requirements
    gtest/cci.20210126 from 'conancenter' - Downloaded
Build requirements packages
    gtest/cci.20210126:c37dc23725d84483088a68c29e2dd7122c328359 - Missing

Installing (downloading, building) binaries...
ERROR: Missing binary: cpr/1.6.2:76fe60a9d5c829a2384b0f578695b5a6357b8acc
ERROR: Missing binary: gtest/cci.20210126:c37dc23725d84483088a68c29e2dd7122c328359
ERROR: Missing binary: jsoncpp/1.9.4:718278bac9f92b77a9a44bfbe1aa00d1c8344d51
ERROR: Missing binary: libcurl/7.78.0:d287dc966931230205222ceabf47400733e72fa3
ERROR: Missing binary: openssl/1.1.1l:c3baf9fae083edda2e0c5ef3337b6a111016a898
ERROR: Missing binary: zlib/1.2.11:c3baf9fae083edda2e0c5ef3337b6a111016a898

Jan

2022

How to fix ModuleNotFoundError: No module named ‘conans’

Problem:

When running conanfile.py or other Python scripts, you see an error message like

Traceback (most recent call last):
  File "/home/myuser/myproject/conanfile.py", line 1, in <module>
    from conans import ConanFile, CMake
ModuleNotFoundError: No module named 'conans'

Solution:

Install conan using one of the recommended methods such as the recommended install via pip

sudo pip3 install conan

Jan

2022

How to fix Failed to restart samba.service: Unit samba.service not found on Debian & Ubuntu

Problem:

When trying to restart the Samba service on Ubuntu or Debian using

sudo systemctl restart samba

you see this error message:

Failed to restart samba.service: Unit samba.service not found.

Solution:

The samba service is called smbd, not samba. Restart it using

sudo systemctl restart smbd

Problem:

Solution:

Problem:

Solution:

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Solution:

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Example:

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Complete error log example

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Solution:

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