[Python-checkins] r69266 - sandbox/trunk/dbm_sqlite/alt/dbdict.py

[raymond.hettinger]

Author: raymond.hettinger
Date: Wed Feb  4 09:28:44 2009
New Revision: 69266

Log:
Add dbdict, a dbm based on a dict subclass.

On open, loads full file into memory.
On close, writes full dict to disk.
Supported file formats: JSON, pickle, or csv



Added:
   sandbox/trunk/dbm_sqlite/alt/dbdict.py   (contents, props changed)

Added: sandbox/trunk/dbm_sqlite/alt/dbdict.py
==============================================================================
--- (empty file)
+++ sandbox/trunk/dbm_sqlite/alt/dbdict.py	Wed Feb  4 09:28:44 2009
@@ -0,0 +1,78 @@
+'''Alternate DB based on a dict subclass
+
+Runs like gdbm's fast mode (all writes all delayed until close).
+While open, the whole dict is kept in memory.  Start-up and
+close time's are potentially long because the whole dict must be
+read or written to disk.
+
+File format is selectable between pickle, json, and csv.
+All three are backed by fast C implementations.
+
+'''
+
+import os, pickle, json, csv
+
+class DictDB(dict):
+
+    def __init__(self, filename, flag='c', mode=None, *args, **kwds):
+        # r=readonly   c=read_write_create_if_needed   n=new_overwrite_previous
+        self.flag = flag
+        self.mode = mode
+        self.filename = filename        
+        if flag != 'n' and os.access(filename, os.R_OK):
+            file = __builtins__.open(filename, 'rb')
+            try:
+                self.update(load(file))
+            finally:
+                file.close()
+        self.update(*args, **kwds)
+
+    def sync(self):
+        if self.flag != 'r':
+            file = __builtins__.open(self.filename, 'wb')
+            try:
+                dump(self, file)
+            finally:
+                file.close()
+            if self.mode:
+                os.chmod(self.filename, self.mode)
+
+    def close(self):
+        self.sync()
+
+def myopen(filename, flag='c', mode=0o666):
+    return DictDB(filename, flag, mode)
+
+def set_csv():
+    global load, dump
+    def load(f):
+        ans = list(csv.reader(f))
+        return ans
+    def dump(self, f):
+        csv.writer(f).writerows(self.items())
+
+def set_json():
+    global load, dump
+    load = json.load
+    def dump(self, f):
+        json.dump(self, f, separators=(',',':'))
+
+def set_pickle():
+    global load, dump    
+    load = pickle.load
+    def dump(self, f):
+        pickle.dump(self, f, -1)
+        
+set_csv()
+
+if __name__ == '__main__':
+    os.chdir('/dbm_sqlite/alt')
+    print(os.getcwd())
+    s = myopen('tmp.shl', 'c')
+    print(s, 'start')
+    s['xyz'] = 'pdq'
+    s['abc'] = '123'
+    s.close()
+    f = __builtins__.open('tmp.shl', 'rb')
+    print (f.read())
+    f.close()