Join lines if character is missing

I have a text file that looks like this:

391  
SMJD50 OJAM 030000  
AAXX 03004  
40272 31557 30000 10054 20034 39323 40165 57009 70500 83100 333  
83830=  

270  
SMJD50 OJAM 030000  
AAXX 03004  
40270 31956 00000 10077 20044 39237 40137 57005 70500=  

242  
SMJD50 OJAM 030000  
AAXX 03004  
40272 31557 30000 10054 20034 39305 40146 57009 70500 83100 333  
83830=  

098  
SMCS01 MROC 030000  
AAXX 03004  
78767 31565 80809 10274 20237 30138 40143 51006 70522 86104  
333 10300 20214 30/// 56000 58011 86820=  

564  
SMAA17 LFVW 030000  
AAXX 03004  
89578 46/// /04// 11396 36678 4//// 5////=  
89577 46/// /0703 11704 35608 4//// 5////=

277  
SMAT01 TKPN 030000  
AAXX 03004  
78859 12580 50916 10269 20209 30172 40176 60001 84202 333 10/// 20///  
58004 84820 83078=   

But I would like to delete some line spacing:

391  
SMJD50 OJAM 030000  
AAXX 03004  
40272 31557 30000 10054 20034 39323 40165 57009 70500 83100 333 83830=  

270  
SMJD50 OJAM 030000  
AAXX 03004  
40270 31956 00000 10077 20044 39237 40137 57005 70500=  

242  
SMJD50 OJAM 030000  
AAXX 03004  
40272 31557 30000 10054 20034 39305 40146 57009 70500 83100 333 83830=  

098  
SMCS01 MROC 030000  
AAXX 03004  
78767 31565 80809 10274 20237 30138 40143 51006 70522 86104 333 10300 20214 30/// 56000 58011 86820=  

564  
SMAA17 LFVW 030000  
AAXX 03004  
89578 46/// /04// 11396 36678 4//// 5////=  
89577 46/// /0703 11704 35608 4//// 5////=

277  
SMAT01 TKPN 030000  
AAXX 03004  
78859 12580 50916 10269 20209 30172 40176 60001 84202 333 10/// 20/// 58004 84820 83078=   

Could anyone help me please? I am using PYTHON.