Added astropy.io.fits.getval functionality

README.md

@@ -111,6 +111,24 @@ fsspec_fits.getdata( in_ref_shutter, ext=1)
 fsspec_fits.getdata( in_ref_shutter, s3_options=s3_options, ext=1)
 ```
 
+### fits.getval
+#### 老写法
+ ```python
+fits.getval(filename, keyword)
+fits.getval(filename, keyword, ext=1)
+```
+usage reference:
+[https://docs.astropy.org/en/stable/io/fits/api/files.html#getdata](https://docs.astropy.org/en/stable/io/fits/api/files.html#getval)  
+
+#### 新写法
+```python
+from csst_fs import fsspec_fits
+fsspec_fits.getval(filename, keyword)
+fsspec_fits.getval(filename, keyword, s3_options=s3_options)
+fsspec_fits.getval(filename, keyword, ext=1)
+fsspec_fits.getval(filename, keyword, s3_options=s3_options, ext=1)
+```
+
 ### header.tofile
 #### 老写法
 ```python

csst_fs/fits/fsspec_fits.py

@@ -9,6 +9,10 @@ def getdata(filename, *args, s3_options=load_s3_options(), **kwargs):
     fileobj = open_fileobj(filename, s3_options, mode='rb')
     return fits.getdata(fileobj, *args, **kwargs)
 
+def getval(filename, keyword, *args, s3_options=load_s3_options(), **kwargs):
+    fileobj = open_fileobj(filename, s3_options, mode='rb')
+    return fits.getval(fileobj, keyword, *args, **kwargs)
+
 def getheader(filename, *args, s3_options=load_s3_options(), **kwargs):
     fileobj = open_fileobj(filename, s3_options, mode='rb')
-    return fits.getheader(fileobj, *args, **kwargs)
\ No newline at end of file
+    return fits.getheader(fileobj, *args, **kwargs)