DEV Community: Ryan Lee

Python 3.7.2 Installation Error: call to undeclared function 'sendfile'

Ryan Lee — Fri, 18 Apr 2025 09:26:41 +0000

I had to install Python 3.7.2 to try out a project. Using pyenv, I encountered a "BUILD FAILED" error. The entire error message is below:

❯ pyenv install 3.7.2
python-build: use openssl@1.1 from homebrew
python-build: use readline from homebrew
Installing Python-3.7.2...
python-build: use tcl-tk from homebrew
python-build: use readline from homebrew
python-build: use zlib from xcode sdk

BUILD FAILED (OS X 15.3.2 using python-build 20180424)

Inspect or clean up the working tree at /var/folders/k0/wdbl3h8d2z3cc7w39t599q380000gn/T/python-build.20250415175136.65981
Results logged to /var/folders/k0/wdbl3h8d2z3cc7w39t599q380000gn/T/python-build.20250415175136.65981.log

Last 10 log lines:
      |                                                      ^
clang -Wno-unused-result -Wsign-compare -Wunreachable-code -DNDEBUG -g -fwrapv -O3 -Wall    -std=c99 -Wextra -Wno-unused-result -Wno-unused-parameter -Wno-missing-field-initializers -Wno-cast-function-type -Werror=implicit-function-declaration   -I. -I./Include -I/usr/local/opt/readline/include -I/usr/local/opt/readline/include -I/Users/ryanlee/.pyenv/versions/3.7.2/include -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include -I/usr/local/opt/readline/include -I/usr/local/opt/readline/include -I/Users/ryanlee/.pyenv/versions/3.7.2/include -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include  -DPy_BUILD_CORE_BUILTIN  -c ./Modules/errnomodule.c -o Modules/errnomodule.o
./Modules/posixmodule.c:8409:15: error: call to undeclared function 'sendfile'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
 8409 |         ret = sendfile(in, out, offset, &sbytes, &sf, flags);
      |               ^
clang -Wno-unused-result -Wsign-compare -Wunreachable-code -DNDEBUG -g -fwrapv -O3 -Wall    -std=c99 -Wextra -Wno-unused-result -Wno-unused-parameter -Wno-missing-field-initializers -Wno-cast-function-type -Werror=implicit-function-declaration   -I. -I./Include -I/usr/local/opt/readline/include -I/usr/local/opt/readline/include -I/Users/ryanlee/.pyenv/versions/3.7.2/include -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include -I/usr/local/opt/readline/include -I/usr/local/opt/readline/include -I/Users/ryanlee/.pyenv/versions/3.7.2/include -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include  -DPy_BUILD_CORE_BUILTIN  -c ./Modules/pwdmodule.c -o Modules/pwdmodule.o
1 error generated.
1 warning generated.
make: *** [Modules/posixmodule.o] Error 1
make: *** Waiting for unfinished jobs....

After some digging around, I found a workaround for 3.7.3:

CFLAGS="-I$(brew --prefix openssl)/include -I$(brew --prefix bzip2)/include -I$(brew --prefix readline)/include -I$(xcrun --show-sdk-path)/usr/include" LDFLAGS="-L$(brew --prefix openssl)/lib -L$(brew --prefix readline)/lib -L$(brew --prefix zlib)/lib -L$(brew --prefix bzip2)/lib" pyenv install --patch 3.7.3 < <(curl -sSL

I figured it might work for 3.7.2. After adapting the command, I got a "zsh: no matches found" error:

> CFLAGS="-I$(brew --prefix openssl)/include -I$(brew --prefix bzip2)/include -I$(brew --prefix readline)/include -I$(xcrun --show-sdk-path)/usr/include" \
  LDFLAGS="-L$(brew --prefix openssl)/lib -L$(brew --prefix readline)/lib -L$(brew --prefix zlib)/lib -L$(brew --prefix bzip2)/lib" \
  pyenv install --patch 3.7.2 < <(curl -sSL https://github.com/python/cpython/commit/8ea6353.patch?full_index=1)
zsh: no matches found: https://github.com/python/cpython/commit/8ea6353.patch?full_index=1

Googling on this error, it turns out that the "?" from the GitHub URI is tripping up the shell interpreter. So we should add a quote around the URI:

curl -sSL 'https://github.com/python/cpython/commit/8ea6353.patch?full_index=1'

The full command:

CFLAGS="-I$(brew --prefix openssl)/include -I$(brew --prefix bzip2)/include -I$(brew --prefix readline)/include -I$(xcrun --show-sdk-path)/usr/include" \
  LDFLAGS="-L$(brew --prefix openssl)/lib -L$(brew --prefix readline)/lib -L$(brew --prefix zlib)/lib -L$(brew --prefix bzip2)/lib" \
  pyenv install --patch 3.7.2 < <(curl -sSL 'https://github.com/python/cpython/commit/8ea6353.patch?full_index=1')

And it worked!

❯ CFLAGS="-I$(brew --prefix openssl)/include -I$(brew --prefix bzip2)/include -I$(brew --prefix readline)/include -I$(xcrun --show-sdk-path)/usr/include" \
  LDFLAGS="-L$(brew --prefix openssl)/lib -L$(brew --prefix readline)/lib -L$(brew --prefix zlib)/lib -L$(brew --prefix bzip2)/lib" \
  pyenv install --patch 3.7.2 < <(curl -sSL 'https://github.com/python/cpython/commit/8ea6353.patch?full_index=1')
python-build: use openssl@1.1 from homebrew
python-build: use readline from homebrew
Installing Python-3.7.2...
patching file 'Misc/NEWS.d/next/macOS/2020-06-24-13-51-57.bpo-41100.mcHdc5.rst'
patching file configure
patching file configure.ac
python-build: use tcl-tk from homebrew
python-build: use readline from homebrew
python-build: use zlib from xcode sdk
Installed Python-3.7.2 to /Users/ryanlee/.pyenv/versions/3.7.2

Don't Miss Out - Amazon EC2 T4g Free Trial Extended to 2025

Ryan Lee — Fri, 20 Dec 2024 07:49:22 +0000

Time flies. It's the end of the year again!

I have been running the EC2 t4g.small instance since 2022 to take advantage of the free trial, which has since been extended twice to December 31, 2024. Yesterday, I went to check the official website of the EC2 T4g Instances to confirm the end date of the trial in preparation for purchasing a savings plan. To my surprise, they have changed the trial end year to 2025! How generous!

Free Trial: Try Amazon EC2 t4g.small instances powered by AWS Graviton2 processors free for up to 750 hours / month until Dec 31st 2025. Refer to the FAQ for additional details.

The best part of this free trial is that, all existing and new customers can take advantage of it, and it is available in addition to free tiers.

There we go. A Christmas present from AWS again.

Who is eligible for the free trial?

As mentioned in the FAQ, all existing and new customers are eligible. However, if you have signed up for consolidated billing, you will have access to one free trial per Organization.

How to join the free trial?

It's as easy as spinning up a t4g.small instance. The bill will take care of itself. It will appear as a $0 item under On-Demand pricing.

One Byte Explainer: Caesar Cipher

Ryan Lee — Sun, 23 Jun 2024 05:59:50 +0000

This is a submission for DEV Computer Science Challenge v24.06.12: One Byte Explainer.

Explainer

Caesar Cipher, or shift cipher, is an encryption technique in which each letter in the given text is replaced by a letter some fixed number of positions (e.g. 3) down the alphabet. Can you decode the following message with this method?

rqh ebwh hasodlqhu

Learn to be Pythonic: List of Multiples of 3

Ryan Lee — Mon, 26 Feb 2024 06:59:14 +0000

Introduction

One of the best ways to learn a programming language is by solving the same challenge with different approaches. Learning to be more Pythonic is no exception. We will solve simple Python programming challenges going from naive and straightforward ways to more Pythonic and smarter approaches. By doing so, we can gain a deeper understanding of what Python offers out of the box and appreciate the flexibility of this beautiful language.

Problem Statement

Create a list of multiples of 3 from 0 to 15 (inclusive)

Solutions

Brute Force

The simplest solution (almost like cheating) is just initializing a list with multiples of 3.

ans = [0, 3, 6, 9, 12, 15]

While Loop with Break

Observing the problem statement, we induced that we can go through each integer i from 0 to 15, and check whether it is a multiple of 3 (i % 3 == 0). A naive implementation is to use an infinite loop (while True) and break out when i is greater than 15.

(This is inspired by a Python quiz question.)

N = 15

ans = []
i = 0
while True:
    if i % 3 == 0:
        ans.append(i)
    if i > N:
        break
    i += 1

While Loop with Condition

A slight improvement to the above solution is to make use of the condition of the while loop: loop whenever i < N + 1.

N = 15

ans = []
i = 0
while i < N + 1:
    if i % 3 == 0:
        ans.append(i)
    i += 1

While Loop Incremented by Steps

You may have observed that, for this particular challenge, we can reduce the number of steps by incrementing i by 3. This also eliminates the check for modulo 3.

N = 15

ans = []
i = 0
while i < N + 1:
    ans.append(i)
    i += 3

For Loop

In fundamental computer science, when the number of iterations is known in advance, a for loop is more appropriate. A very useful iterator in Python for this use case is range.

N = 15

ans = []
for i in range(N + 1):
    if i % 3 == 0:
        ans.append(i)

This is cleaner and more expressive than the while loop.

List Comprehension

To further refactor the solution, we turn to a feature of Python called “list comprehension”. It provides a concise way to create a list from an iterator. This is when the solution starts to be more “Pythonic”.

N = 15

ans = [i for i in range(N + 1) if i % 3]

Filter

An alternative solution without the for loop is using the filter function. It is handy for filtering an iterator through a test function. In this example, the test function is constructed with lambda.

N = 15

ans = list(filter(lambda x: x % 3 == 0, range(N + 1)))

Filter with Predefined Function

The lambda function is convenient but lacks context and compromises readability. A better version of the filter solution is to predefine the test function.

N = 15

def is_mul_3(x):
    return x % 3 == 0

ans = list(filter(is_mul_3, range(N + 1)))

Range with Steps

In a previous solution, we optimized the loop by reducing the number of iterations by incrementing the counter by a step of 3. This is possible with the range function by taking advantage of its optional third argument, step. It tells range to increment the counter by the step amount. As such, we can remove the filter altogether.

N = 15

ans = list(range(0, N + 1, 3))

Conclusion

By finding different ways to solve a simple problem, we have already touched on the key Python concepts of list, while, break, for, range, filter, lambda, and list comprehension. The earlier solutions are more naive and not recommended as best practices, but they are still good exercises to solidify the fundamentals. Between the more Pythonic list comprehension and functional style, it will require an experienced programmer to weigh the pros and cons to balance readability, efficiency, and maintainability. Lastly, using the step argument from range might seem obvious, but it requires deeper knowledge of Python and may confuse peer programmers trying to maintain the code. Therefore, it is essential for a programmer to share his or her knowledge with others, so that the team can grow as a whole, thereby increasing the efficiency (or Pythonicity?) of a software project.

Can you find other creative ways to solve this challenge?

Further resources:

Migrating Amazon SNS from Legacy FCM API to HTTP V1 API

Ryan Lee — Tue, 23 Jan 2024 09:50:04 +0000

Introduction

On a work project, we use Amazon SNS to send push notifications to a mobile app registered with Google's Firebase Cloud Messaging (FCM). Although Google was deprecating the Legacy FCM API at that time, SNS did not yet support the new HTTP V1 API. Last weekend, I received an email from AWS that SNS now supports the new API (yay!).

Procedures

This tutorial is written based on the steps I took to migrate to the V1 API. Please adjust accordingly.

Getting the Service JSON
1. Log in to the Firebase console.
2. Select the project that receives API calls from SNS.
3. At the top left corner, click on the gear icon, and select Project Settings.
4. At the top navigation under Project Settings, pick Service accounts.
5. Click Generate new private key. A popup shows up reminding you to secure the key. Click *Generate key.
6. The key should be downloaded.
Uploading the Service JSON
1. Log in to the Amazon SNS console.
2. Select Push notifications (under Mobile) from the left side menu. Pick the appropriate platform application.
3. Edit the platform application. At the authentication method, pick Token (recommended). It will ask you to upload a service.json file. Pick the key downloaded previously from the Firebase console.
4. Save changes.
Testing
1. At the Platform application page, click on the link of an endpoint from the list below. At the top right-hand corner, click Publish message.
2. At the Message body section, pick Custom payload and input the GCM message payload according to your platform (mine is Android).
3. Check the app for notifications.
4. To verify that it is using the new API, go back to the Firebase console Service accounts tab (refer to step 1.4). Click Manage service account permissions at the top-right-hand corner.
5. At the Service accounts management page, locate the account associated with Firebase Admin SDK. Click the dots menu under Action on the right, and pick View metrics.
6. Verify there were actions when the message was being sent.

Congratulations!

The migration is now complete. You may have to update the message payload to the new message format. Start exploring the multiplatform messaging capability now!

Extended reading

AWS Boto3: Clients vs Resources - Amazon DynamoDB

Ryan Lee — Sun, 21 Jan 2024 09:44:48 +0000

Recently, my colleague brought up the difficulty of using the AWS SDK for Python (Boto3) while working with DynamoDB, especially the cumbersome mapping of AttributeValue objects on the Table operations. One of the easiest ways to get around this difficulty is to switch from the clients interface to the resources interface.

It is important to know the key difference between clients and resources. From the definition of the Boto3 documentation:

Clients provide a low-level interface to AWS whose methods map close to 1:1 with service APIs.

Resources represent an object-oriented interface to Amazon Web Services (AWS). They provide a higher-level abstraction than the raw, low-level calls made by service clients.

Let's quickly write a script to demonstrate the difference in the responses:

import boto3
import simplejson

def print_items(desc, response):
    items = response.get('Items')
    items_json = simplejson.dumps(items, indent=4)
    print(f'{desc}:', items_json, sep='\n')

ddb_table_name = 'test'

# DynamoDB client
ddb_client = boto3.client('dynamodb')

# Scan the table
response = ddb_client.scan(TableName=ddb_table_name)
print_items('client', response)

print('\n')

# DynamoDB resource
ddb_resource = boto3.resource('dynamodb')

# Scan the table
response = ddb_resource.Table(ddb_table_name).scan()
print_items('resource', response)

The output:

client:
[
    {
        "datetime": {
            "S": "2024-01-20T00:01:02"
        },
        "id": {
            "N": "1"
        },
        "data": {
            "L": [
                {
                    "M": {
                        "amount": {
                            "N": "40"
                        }
                    }
                },
                {
                    "M": {
                        "amount": {
                            "N": "56"
                        }
                    }
                }
            ]
        }
    }
]


resource:
[
    {
        "datetime": "2024-01-20T00:01:02",
        "id": 1,
        "data": [
            {
                "amount": 40
            },
            {
                "amount": 56
            }
        ]
    }
]

Notice the simplicity of the second output. The abstraction of the resources interface deserialized the low-level raw response of the AWS service API.

In most cases, the resources interface can be used over the low-level clients for the abstraction benefits. However, as stated at the top of the resources interface documentation:

The AWS Python SDK team does not intend to add new features to the resources interface in boto3".

Therefore, it is essential to compare both interfaces to determine whether the resources interface is sufficient for your use case.

In a future post, I will explore another method to work with the AttributeValue maps in Boto3.

Fixing MSVCP140_ATOMIC_WAIT.dll Not Found

Ryan Lee — Wed, 17 Jan 2024 06:10:18 +0000

One of my colleagues recently encountered an error trying to open an Excel workbook on Sharepoint via the "Open in Desktop App" button. The screenshot of the error is below:

The error wasn't triggered when starting Excel normally, nor opening the same spreadsheet from OneDrive Desktop.

Upon Googling, I found results offering the direct download of this DLL, but I am not downloading DLLs from unknown sources! Other search results relate to gaming. One of the results suggested repairing Visual C++, but that didn't help.

Frustrated, I tried to repair and update a few Microsoft software. It was finally fixed by repairing Microsoft Office.

Lesson Learned

In conclusion, if I tried the fix suggested by the error message before searching the web for solutions, I would have saved time and frustration.

Extended reading

https://www.reddit.com/r/Xcom/comments/osgaal/msvcp140_atomic_waitdll_was_not_found/

DEV Community: Ryan Lee

Python 3.7.2 Installation Error: call to undeclared function 'sendfile'

Don't Miss Out - Amazon EC2 T4g Free Trial Extended to 2025

Who is eligible for the free trial?

How to join the free trial?

One Byte Explainer: Caesar Cipher

Explainer

Learn to be Pythonic: List of Multiples of 3

Introduction

Problem Statement

Solutions

Brute Force

While Loop with Break

While Loop with Condition

While Loop Incremented by Steps

For Loop

List Comprehension

Filter

Filter with Predefined Function

Range with Steps

Conclusion

Further resources:

Migrating Amazon SNS from Legacy FCM API to HTTP V1 API

Introduction

Procedures

Congratulations!

Extended reading

AWS Boto3: Clients vs Resources - Amazon DynamoDB

Further reading

Fixing MSVCP140_ATOMIC_WAIT.dll Not Found

Lesson Learned

Extended reading