python - My unit checking variable isn't reading the input properly, when I put cm in as input the program sends the boolean to the else -

when enter cm ucheck variable program prints string in else condition

ucheck=input(print('unit?')) #<--i enter 'cm' here if ucheck=='nm':     wave=wave if ucheck=='cm': #<--it seems skip boolean     wave=wave*(10**7) if ucheck=='mm':     wave=wave*(10**6) if ucheck=='m':     wave=wave*(10**9) else:     print('invalid unit! valid units are: nm, mm, cm, m.') #<-- , prints     frequency() 

your if statements separate. if first 1 true, you'll still check second one, , third one, , fourth one, , since first 1 true, else block executed.

change them elif , code should work:

ucheck = input('unit? ')  if ucheck == 'nm':     wave = wave elif ucheck == 'cm':     ... 

also, better way dictionary:

units = {     'nm': 1,     'mm': 10**6,     'cm': 10**7,     'm': 10**9 }  unit = input('unit? ')  if unit in units:     wave *= units[unit] else:     print('invalid unit! valid units are: ' + ', '.join(units))     frequency()