programming
Feature Fortran
Fortran 95 		c Python IDL
Compiler f77 (g77) -o .f
f95 (gfortran) -o .f90 		cc (gcc) -o .c not compiled, execute with
python .py or use
#/usr/bin/env python 		within IDL, .run progname
Overall structure program name
variable declarations
program statements
end 		include statments
main() {
 program statements
 return(0);
} 		#!/usr/bin/env python
(to allow import,
def main :
 program statements
if __name__ == "__main__" :
 main()
)
comments ! (C in f77) // /*...*/ # ;
line continuation / termination f95: & at end of line
f77: character in column 6 		lines must end with ; implicit continuation using
expression in parentheses 		$ at end of line
variables implicit declaration (i-o are integer),
but implicit none is preferred
character, real, integer, logical
f95:
{TYPE} :: variable[=value] (f95)
can be initialized
INTEGER :: i=0
REAL :: f=3.4
CHARACTER(n) :: variable (f95 string of length n)
f77:
{TYPE} variable
   INTEGER i
   REAL f
  CHARACTER*n variable
initialization through DATA statement 		must be declared (char, short,
int, float, double);
can be initialized
int i,j,k=0;
real o,p=3.9;
char str[20]; 		not declared not declared
type conversion
arrays e.g., real arr(m,n) e.g., float arr[n][m]; e.g., numpy.zeros(n,m),
numpy.array([[a,b,c,d][e,f,g]]),
numpy.arange(n) 		e.g., fltarr(m,n), indgen(n)
dynamic memory allocation allocate, deallocate, after giving variable allocatable attribute malloc, free
structures (derived data types)
type mytype
  character(12):: cval = ''
  real :: rval = 0.
end type mytype
type (mytype) :: var
var%name = 'test'
var%ra = 1. 		struct {
  char cval[12];
  real rval;
} var;
strcpy(var.name, "test");
var.ra = 1.; 		(dictionaries, see also lists)
var = { 'name' : 'test', ra : 1. }
print var['name'], var['test'] 		var = { name: 'test', ra: 1. }
print,var.name, var.test
structure arrays type (mytype), dimension=nelem :: var
 sarray = np.zeros(nelem,
 dtype=[('name','a12'),('ra','f4'),('dec','f4')])
sarray = np.zeros(nelem,
 dtype={'names': ('name', 'ra', 'dec'),
 'formats': ('S12', 'f4', 'f4')}) 		sarray = replicate (str, nelem)
operators
add, sub, mul, div, expon 		+, -, *, /, ** +, -, *, /, pow(), +=, -=, *=, /=, ++, -- +, -, *, /, **, +=, -=, *=, /=, ++, -- +, -, *, /, ^, +=, -=, *=, /=, ++, --
bitwise operators
and, or, xor, not 		iand, ior, ieor, not &, |, ^, ~ &, |, ^, ! and, or, xor, not
string operators //, len, str(i1:i2) strcat(str,add),
strcpy(dest,src), strncpy(dest,src,n)
strlen(str),
strncpy(sub,str+i1,(i2-i1+1)) 		+, str[i1:i2] (string slice,
but string is immutable) 		+, strpos, strmid, strsplit, strlen
matrix operations dot_product(a,b), matmul(a,b) #, ##
conditionals if ( condition) then
  statements
else
  statements
end if
(for a single statement, can
omit then and put statement
on same line as if)
(see also SELECT CASE) 		if (condition) {
  statements
} else {
  statements
}
(see also switch statement) 		if ( condition ) :
  statements
else :
  statements
(extent of conditional statements
specified by indentation) 		if (condition) then begin
  statements
endif else begin
  statements
endelse
(see also CASE statment)
conditions
(logical operators) 		.eq. (==), .ne. (/=), .gt. (>), ge. (>=), .lt. (<), .le. (<=), .and., .or. ==, !=, >, >=, <, <=, &&, || == != > >= < <=, and, or, not eq, ne, gt, ge, lt, le, &&, ||, ~
looping do i=start,end,increment
  statements
end do 		for ( i=start; condition; action) {
  statements
} 		for i in ( list) :
  statements
(extent of loop statements
specified by indentation) 		for i=start,end,increment
  statements
endfor
looping with condition do while (condition)
  statements
enddo 		while (condition) {
  statements
} 		while (condition):
  statements
(extent of loop statements
specified by indentation) 		while (condition)begin
  statements
endwhile
simple output print *, 'characters', string, variable printf("characters: %s %d\n",string,variable); print 'characters', string, variable print,'characters: ', string,variable
formatted output e.g.,
CHARACTER :: FORMAT='(i8,f8.2)'
PRINT FORMAT, i,f
formats: in, fn.n, an, nx
reference 		char format[] = "%2d %8.2f\n";
printf(format,i,f);
formats: %nd, %n.nf, %ns 		'{:8d}asdfad{:8.2f}'.format(i,f)
formats: {:nd}, {:n.nf}, {:ns} reference 		print,format='(fortranlike)'
simple reading from terminal and file terminal:
READ *, var
file:
OPEN(lun,FILE=file)
IERR=0
DO WHILE ( IERR == 0 )
 READ(lun,format, IOSTAT=ierr) var
 PRINT *, line
CLOSE(lun) 		terminal:
scanf("%s",char *);
file:
#include <stdio.h>
char string[100];
FILE *fp;
fp=fopen(file,"[rwa]");
while(fgets(string, 100, fp)) {
  printf("%s\n", string);
}
fclose(fp); 		terminal:
s=raw_input('prompt')
file:
f=open(file,'[rwa]') (read,write,append)
s=f.readline()
f.close(),
alternatively:
for line in f:
  print line 		file:
line=''
openr,lun,file,/get_lun
while not EOF(lun) do begin
 readf,lun,line
 print,line
end
free_lun,lun
higher level ASCII file reading routines data = numpy.loadtxt(file,
 dtype=[('name','a12'),('ra',f4),('dec','f4')])

data = astropy.io.ascii(file) 		readcol,file,name,ra,dec,format='(a,f,f)'
read_ascii(file,template)
FITS I/O routines import astropy.io.fits as fits
hdus=fits.open(file)
hdus[0].header
hdus[0].data