演示地址：
https://replit.com/@PaoloAmoroso/spacestills
这是一个具有GUI的简单系统，它访问feed流并从Web下载数据。该程序仅需350行代码，并依赖于一些开源的Python库。
关于程序
Spacestills会定期从feed流中下载NASA TV静止帧并将其显示在GUI中。
该程序可以校正帧的纵横比，并将其保存为PNG格式。它会自动下载最新的帧，并提供手动重新加载，禁用自动重新加载或更改下载频率的选项。
Spacestillsis是一个比较初级的版本，但是它可以做一些有用的事情：捕获并保存NASA TV直播的太空事件图像。太空爱好者经常在社交网络或论坛共享他们从NASA TV手动获取的屏幕截图。Spacestills节省了使用屏幕捕获工具的时间，并保存了可供共享的图像文件。您可以在Replit上在线运行Spacestills。
开发环境
笔者用Replit开发了Spacestills。Replit是云上的开发，部署和协作环境，它支持包括Python在内的数十种编程语言和框架。作为Chrome操作系统和云计算爱好者，笔者非常喜欢Replit，因为它可以在浏览器中完全正常运行，无需下载或安装任何内容。
资源和依赖包
Spacestills依赖于一些外部资源和Python库。
NASA TV feed 流
肯尼迪航天中心的网站上有一个页面，其中包含精选的NASA视频流，包括NASA电视公共频道。feed流显示最新的静止帧并自动更新。
每个feed都带有三种尺寸的帧，Spacestills依赖于具有704×408像素帧的最大NASA TV feed流。最大更新频率为每45秒一次。因此，检索最新的静止帧就像从feed流的URL下载JPEG图像一样简单。
原始图像被垂直拉伸，看起来很奇怪。因此，该程序可以通过压缩图像并生成未失真的16：9版本来校正纵横比。
Python
因PySimpleGUI的原因需要安装 Python 3.6 版本。
第三方库
- Pillow：图像处理
- PySimpleGUI：GUI框架（Spacestills使用Tkinter后端）
- Request：HTTP请求
完整代码
from io import BytesIO from datetime import datetime, timedelta from pathlib import Path import requests from requests.exceptions import Timeout from PIL import Image import PySimpleGUI as sg FEED_URL = \'https://science.ksc.nasa.gov/shuttle/countdown/video/chan2large.jpg\' # Frame size without and with 16:9 aspect ratio correction WIDTH = 704 HEIGHT = 480 HEIGHT_16_9 = 396 # Minimum, default, and maximum autoreload interval in seconds MIN_DELTA = 45 DELTA = MIN_DELTA MAX_DELTA = 300 class StillFrame(): \"\"\"Holds a still frame. The image is stored as a PNG PIL.Image and kept in PNG format. Attributes ---------- image : PIL.Image A still frame original : PIL.Image Original frame with wchich the instance is initialized, cached in case of resizing to the original size Methods ------- bytes : Return the raw bytes resize : Resize the screenshot new_size : Calculate new aspect ratio \"\"\" def __init__(self, image): \"\"\"Convert the image to PNG and cache the converted original. Parameters ---------- image : PIL.Image Image to store \"\"\" self.image = image self._topng() self.original = self.image def _topng(self): \"\"\"Convert image format of frame to PNG. Returns ------- StillFrame Frame with image in PNG format \"\"\" if not self.image.format == \'PNG\': png_file = BytesIO() self.image.save(png_file, \'png\') png_file.seek(0) png_image = Image.open(png_file) self.image = png_image return self def bytes(self): \"\"\"Return raw bytes of a frame image. Returns ------- bytes Byte stream of the frame image \"\"\" file = BytesIO() self.image.save(file, \'png\') file.seek(0) return file.read() def new_size(self): \"\"\"Return image size toggled between original and 16:9. Returns ------- 2-tuple New size \"\"\" size = self.image.size original_size = self.original.size new_size = (WIDTH, HEIGHT_16_9) if size == original_size else (WIDTH, HEIGHT) return new_size def resize(self, new_size): \"\"\"Resize frame image. Parameters ---------- new_size : 2-tuple New size Returns ------- StillFrame Frame with image resized \"\"\" if not(self.image.size == new_size): self.image = self.image.resize(new_size) return self def make_blank_image(size=(WIDTH, HEIGHT)): \"\"\"Create a blank image with a blue background. Parameters ---------- size : 2-tuple Image size Returns ------- PIL.Image Blank image \"\"\" image = Image.new(\'RGB\', size=size, color=\'blue\') return image def download_image(url): \"\"\"Download current NASA TV image. Parameters ---------- url : str URL to download the image from Returns ------- PIL.Image Downloaded image if no errors, otherwise blank image \"\"\" try: response = requests.get(url, timeout=(0.5, 0.5)) if response.status_code == 200: image = Image.open(BytesIO(response.content)) else: image = make_blank_image() except Timeout: image = make_blank_image() return image def refresh(window, resize=False, feed=FEED_URL): \"\"\"Display the latest still frame in window. Parameters ---------- window : sg.Window Window to display the still to feed : string Feed URL Returns ------- StillFrame Refreshed screenshot \"\"\" still = StillFrame(download_image(feed)) if resize: still = change_aspect_ratio(window, still, new_size=(WIDTH, HEIGHT_16_9)) else: window[\'-IMAGE-\'].update(data=still.bytes()) return still def change_aspect_ratio(window, still, new_size=(WIDTH, HEIGHT_16_9)): \"\"\"Change the aspect ratio of the still displayed in window. Parameters ---------- window : sg.Window Window containing the still new_size : 2-tuple New size of the still Returns ------- StillFrame Frame containing the resized image \"\"\" resized_still = still.resize(new_size) window[\'-IMAGE-\'].update(data=resized_still.bytes()) return resized_still def save(still, path): \"\"\"Save still to a file. Parameters ---------- still : StillFrame Still to save path : string File name Returns ------- Boolean True if file saved with no errors \"\"\" filename = Path(path) try: with open(filename, \'wb\') as file: file.write(still.bytes()) saved = True except OSError: saved = False return saved def next_timeout(delta): \"\"\"Return the moment in time right now + delta seconds from now. Parameters ---------- delta : int Time in seconds until the next timeout Returns ------- datetime.datetime Moment in time of the next timeout \"\"\" rightnow = datetime.now() return rightnow + timedelta(seconds=delta) def timeout_due(next_timeout): \"\"\"Return True if the next timeout is due. Parameters ---------- next_timeout : datetime.datetime Returns ------- bool True if the next timeout is due \"\"\" rightnow = datetime.now() return rightnow >= next_timeout def validate_delta(value): \"\"\"Check if value is an int within the proper range for a time delta. Parameters ---------- value : int Time in seconds until the next timeout Returns ------- int Time in seconds until the next timeout bool True if the argument is a valid time delta \"\"\" isinteger = False try: isinteger = type(int(value)) is int except Exception: delta = DELTA delta = int(value) if isinteger else delta isvalid = MIN_DELTA <= delta <= MAX_DELTA delta = delta if isvalid else DELTA return delta, isinteger and isvalid LAYOUT = [[sg.Image(key=\'-IMAGE-\')], [sg.Checkbox(\'Correct aspect ratio\', key=\'-RESIZE-\', enable_events=True), sg.Button(\'Reload\', key=\'-RELOAD-\'), sg.Button(\'Save\', key=\'-SAVE-\'), sg.Exit()], [sg.Checkbox(\'Auto-reload every (seconds):\', key=\'-AUTORELOAD-\', default=True), sg.Input(DELTA, key=\'-DELTA-\', size=(3, 1), justification=\'right\'), sg.Button(\'Set\', key=\'-UPDATE_DELTA-\')]] def main(layout): \"\"\"Run event loop.\"\"\" window = sg.Window(\'Spacestills\', layout, finalize=True) current_still = refresh(window) delta = DELTA next_reload_time = datetime.now() + timedelta(seconds=delta) while True: event, values = window.read(timeout=100) if event in (sg.WIN_CLOSED, \'Exit\'): break elif ((event == \'-RELOAD-\') or (values[\'-AUTORELOAD-\'] and timeout_due(next_reload_time))): current_still = refresh(window, values[\'-RESIZE-\']) if values[\'-AUTORELOAD-\']: next_reload_time = next_timeout(delta) elif event == \'-RESIZE-\': current_still = change_aspect_ratio( window, current_still, current_still.new_size()) elif event == \'-SAVE-\': filename = sg.popup_get_file( \'File name\', file_types=[(\'PNG\', \'*.png\')], save_as=True, title=\'Save image\', default_extension=\'.png\') if filename: saved = save(current_still, filename) if not saved: sg.popup_ok(\'Error while saving file:\', filename, title=\'Error\') elif event == \'-UPDATE_DELTA-\': # The current cycle should complete at the already scheduled time. So # don\'t update next_reload_time yet because it\'ll be taken care of at the # next -AUTORELOAD- or -RELOAD- event. delta, valid = validate_delta(values[\'-DELTA-\']) if not valid: window[\'-DELTA-\'].update(str(DELTA)) window.close() del window if __name__ == \'__main__\': main(LAYOUT)
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