Improves code readability

slither/printers/summary/evm.py

@@ -5,12 +5,15 @@
 import logging
 from slither.printers.abstract_printer import AbstractPrinter
 try:
+    # Avoiding the addition of evm_cfg_builder as permanent dependency
     from evm_cfg_builder.cfg import CFG
 except ImportError:
-    logger.error("ERROR: in order to use evm printer, you need to install evm-cfg-builder")
-    logger.error("pip install evm-cfg-builder")
+    logger.error("To use evm printer, you need to install evm-cfg-builder from ToB")
+    logger.error("Documentation: https://github.com/crytic/evm_cfg_builder")
+    logger.error("Installation: pip install evm-cfg-builder")
     sys.exit(-1)
 
+    
 class PrinterEVM(AbstractPrinter):
 
     ARGUMENT = 'evm'
@@ -18,6 +21,7 @@ class PrinterEVM(AbstractPrinter):
 
     WIKI = 'https://github.com/trailofbits/slither/wiki/Printer-documentation#evm'
 
+    
     def output(self, _filename):
         """
             _filename is not used
@@ -29,10 +33,12 @@ class PrinterEVM(AbstractPrinter):
 
         for contract in self.slither.contracts_derived:
             print('Contract {}'.format(contract.name))
+            
             contract_file = self.slither.source_code[contract.source_mapping['filename_absolute']].encode('utf-8')
             contract_file_lines = open(contract.source_mapping['filename_absolute'],'r').readlines()
             contract_cfg = evm_info['cfg', contract.name]
             contract_pcs = evm_info['mapping', contract.name]
+
             for function in contract.functions:
                 print(f'\tFunction {function.canonical_name}')
                 for node in function.nodes:
@@ -43,6 +49,7 @@ class PrinterEVM(AbstractPrinter):
                     node_pcs = contract_pcs.get(node_source_line, [])
                     for pc in node_pcs:
                         print('\t\t\t0x{:x}: {}'.format(int(pc), contract_cfg.get_instruction_at(pc)))
+                        
             for modifier in contract.modifiers:
                 print(f'\tModifier {modifier.canonical_name}')
                 for node in modifier.nodes:
@@ -53,13 +60,16 @@ class PrinterEVM(AbstractPrinter):
                     for pc in node_pcs:
                         print('\t\t\t0x{:x}: {}'.format(int(pc), contract_cfg.get_instruction_at(pc)))
 
+                        
     def _extract_evm_info(self, slither):
-        '''
+        """
         Extract evm information for all derived contracts using evm_cfg_builder
 
         Returns: evm CFG and Solidity source to Program Counter (pc) mapping
-        '''
+        """
+        
         evm_info = {}
+        
         for contract in slither.contracts_derived:
             contract_bytecode_runtime = slither.crytic_compile.bytecode_runtime(contract.name)
             contract_srcmap_runtime = slither.crytic_compile.srcmap_runtime(contract.name)
@@ -69,34 +79,45 @@ class PrinterEVM(AbstractPrinter):
                                                                                  contract_srcmap_runtime, slither,
                                                                                  contract.source_mapping['filename_absolute'])
         return(evm_info)
+
     
     def _generate_source_to_evm_ins_mapping(self, evm_instructions, srcmap_runtime, slither, filename):
-        '''
+        """
         Generate Solidity source to EVM instruction mapping using evm_cfg_builder:cfg.instructions and solc:srcmap_runtime
 
         Returns: Solidity source to EVM instruction mapping
-        '''
+        """
+        
         source_to_evm_mapping = {}
         file_source = slither.source_code[filename].encode('utf-8')
         prev_mapping = []
+        
         for idx, mapping in enumerate(srcmap_runtime):
             # Parse srcmap_runtime according to its format
             # See https://solidity.readthedocs.io/en/v0.5.9/miscellaneous.html#source-mappings
+            
             mapping_item = mapping.split(':')
             mapping_item += prev_mapping[len(mapping_item):]
+            
             for i in range(len(mapping_item)):
                 if mapping_item[i] == '':
                     mapping_item[i] = int(prev_mapping[i])
+                    
             offset, length, file_id, _ = mapping_item
+            
             if file_id == '-1':
                 # Internal compiler-generated code snippets to be ignored
                 # See https://github.com/ethereum/solidity/issues/6119#issuecomment-467797635
                 continue
+            
             offset = int(offset)
             line_number = file_source[0:offset].count("\n".encode("utf-8")) + 1
-            prev_mapping = mapping_item
+            
             # Append evm instructions to the corresponding source line number
             # Note: Some evm instructions in mapping are not necessarily in program execution order
             # Note: The order depends on how solc creates the srcmap_runtime
             source_to_evm_mapping.setdefault(line_number, []).append(evm_instructions[idx].pc)
+            
+            prev_mapping = mapping_item
+            
         return(source_to_evm_mapping)